Changes in Atmospheric, Meteorological, and Ocean Parameters Associated with the 12 January 2020 Taal Volcanic Eruption

: The Taal volcano erupted on 12 January 2020, the ﬁrst time since 1977. About 35 mild earthquakes (magnitude greater than 4.0) were observed on 12 January 2020 induced from the eruption. In the present paper, we analyzed optical properties of volcanic aerosols, volcanic gas emission, ocean parameters using multi-satellite sensors, namely, MODIS (Moderate Resolution Imaging Spectroradiometer), AIRS (Atmospheric Infrared Sounder), OMI (Ozone Monitoring Instrument), TROPOMI (TROPOspheric Monitoring Instrument) and ground observations, namely, Argo, and AERONET (AErosol RObotic NETwork) data. Our detailed analysis shows pronounced changes in all the parameters, which mainly occurred in the western and south-western regions because the airmass of the Taal volcano spreads westward according to the analysis of airmass trajectories and wind directions. The presence of ﬁner particles has been observed by analyzing aerosol properties that can be attributed to the volcanic plume after the eruption. We have also observed an enhancement in SO 2 , CO, and water vapor, and a decrease in Ozone after a few days of the eruption. The unusual variations in salinity, sea temperature, and surface latent heat ﬂux have been observed as a result of the ash from the Taal volcano in the south-west and south-east over the ocean. Our results demonstrate that the observations combining satellite with ground data could provide important information about the changes in the atmosphere, meteorology, and ocean parameters associated with the Taal volcanic eruption.


Introduction
Active volcanoes exist throughout the world and are distributed in different continents. In the past, more than 1500 volcanoes have erupted [1]. Volcanic eruptions are one of the deadly natural disasters that may cause extensive damage by thick hot ashes and lava flows. The associated emissions have long term impacts on agriculture, glaciers, aviation, ecology, environment, air quality, human health, solar activity, atmosphere, and ocean water when a volcano is located near the ocean coast [2][3][4][5][6][7][8][9][10][11]. The impact of a volcanic ash plume has been observed in the Asian summer monsoon associated with the Sarychev eruption in 2009 [12]. During a volcanic eruption, several gases are emitted, and generally, the amount of sulfur dioxide (SO 2 ) is very high. The gases from the volcano are dispersed On 12 January 2020 at 2.30 p.m. (local time), an explosive eruption produced a giant plume of volcanic ash up to 15 km in the atmosphere and extending up to about 67 km south of the capital city of Manila [50] and beyond, up to the city of Quezon about 70 km away from the location of the Taal volcano. Over 50,000 people were affected, and Manila International airport suspended all flights. The Taal island and surrounding provinces were evacuated [50]. Within 24 h of the eruption, about 450 earthquakes were felt with the emergence of fissures and receding of the surrounding lake. The observed seismic activities suggest a rise of magma from deep in the earth [50].
The Taal volcano is an active volcano located on the southwest of the Luzon island in the Philippines. Figure 1 shows the geolocation of Taal Volcano and its surroundings, with ocean water close to the volcano. Taal Volcano is surrounded by the Taal lake outside and the main crater lake inside. Historically, over a 10℃ increase in temperature of the crater lake has been observed before the eruption in September 1965 [51].
Taal Volcano was classified as "DECADE VOLCANOES" by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI). A total of 33 historical eruptions have been recorded, excluding the newest one [52], but the latest study has shown that only 24 of the 33 historic events are confirmed, and the other nine should be considered for reassessment [53]. The last eruption of the Taal volcano occurred on 3-4 October 1977, and afterward, it remained quiet, but more than 20 earthquake swarms were recorded until 12 January 2020 [53]. No other signals were observed about an impending volcanic eruption, which occurred on 12 January 2020. Details of the volcano and associated links are available from the US National Museum of Natural History's Global Volcanism Program (https://volcano.si.edu/volcano.cfm?vn = 273070).  Taal Volcano was classified as "DECADE VOLCANOES" by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI). A total of 33 historical eruptions have been recorded, excluding the newest one [52], but the latest study has shown that only 24 of the 33 historic events are confirmed, and the other nine should be considered for reassessment [53]. The last eruption of the Taal volcano occurred on 3-4 October 1977, and afterward, it remained quiet, but more than 20 earthquake swarms were recorded until 12 January 2020 [53]. No other signals were observed about an impending volcanic eruption, which occurred on 12 January 2020. Details of the volcano and associated links are available from the US National Museum of Natural History's Global Volcanism Program (https://volcano.si.edu/volcano.cfm?vn=273070).

Volcano monitoring
Earlier, in December 1952, monitoring of Taal Volcano started, and the first volcanological station was established by the Commission on Volcanology (COMVOL) in Brgy. The station was equipped with a three-components low sensitivity seismograph: a water-tube tiltmeter, thermometers, and short-wave radio transmitters. On 28 September 1965, all the instruments were destroyed due to the onset of a phreatomagmatic phase of the Mt. Tabaro eruption. In 1966, a new Pira-piraso station was established on the northern shore of Volcano Island with seismographs and a tiltmeter, these instruments were updated in 1968 and again in 1970. At the northern shore of Taal Lake, Buco observatory was constructed from 1969 to 1970, which was handed over to COMVOL after completion with a similar set of instruments and a speed boat. The observatory was reconstructed in 2016 after severe damage from a blown-down century-old acacia tree during the passage of Typhoon Glenda in 2015 (https: //www.phivolcs.dost.gov.ph/index.php/volcano-hazard/volcano-monitoring2/volcano-observatory).
During the last 40 years, no eruptive activity was recorded; given the past eruption history, an unusual quiescence period was realized by the scientists. Seismological [54,55], geochemical [56], electromagnetic [55,57], thermal [52,58], and InSAR crustal deformation measurement [59] techniques were used to monitor activities of the Taal volcano. Efforts were made to map the 3-D structure and monitor the volcanic activities and observations of geophysical parameters (magnetic, electric, tilt, resistivity, ground and water temperature). All these geophysical parameters were recorded at the field sites and telemetered to PHIVOLCS (The Philippine Institute of Volcanology and Seismology). A shallow magmatic source located at a depth 4-6 km below the current Main Crater Lake on Volcano Island were delineated [52,55,57].
Due to the long gap in eruption period, it was expected that the next eruption would be large (volcanic explosive index-VEI ≥ 4) and more likely that the eruption would occur from another cone surrounding the main crater (PHIVOLCS http://www.phivolcs.dost.gov.ph/). Through an international cooperative program involving teams from Japan, France, USA, Greece, Italy, and Belgium, training to PHIVOLCS members about the installation techniques, analysis of electromagnetic data, and ways to monitor the volcano were given.

Earthquake activities around Taal Volcano
The Taal volcano area is seismically active. Figure 2a shows the frequency of mild earthquakes within a radius of 150 km around the Taal volcano, downloaded from the USGS (United States Geological Survey) website (https://earthquake.usgs.gov/earthquakes) during the period 25 January 2000 to 10 February 2020. The two largest earthquakes occurred on 8 October 2004 with a magnitude of 6.5 and a focal depth of 105 km, and another earthquake on 11 August 2017 with a magnitude of 6.2 and a focal depth of 172 km. Both these earthquakes were located within 50 km around the Taal volcano (PHIVOLCS http://www.phivolcs.dost.gov.ph/). Figure 2b shows the spatial distribution of the earthquake epicenters with a magnitude greater than 4.0 mb within a 50 km radius around the Taal volcano during the period 1 November 2019 -9 March 2020. On the day of the Taal eruption, a total number of 35 earthquakes (magnitude with 4.2-4.7 mb) occurred and continued for 24 h. Figure 2c shows the temporal distribution of earthquake activities (magnitude greater than 4.0 mb) within a 50 km radius around the Taal volcano between 1 November 2019 and 9 March 2020 from the USGS website. Prior to 12 January 2020, four earthquakes (magnitude 4.8, 4.0, 4.4, and 4.1 mb) occurred, respectively, on 15 November 2019, and 2, 9, and 24 December 2019. It is difficult for us to access a detailed catalog of earthquakes, so we cannot comment on the frequency of small earthquakes. March 2020. Yellow dots show the distribution of earthquake epicenters. A total of 35 earthquakes occurred on 12 January 2020, and afterward, 18 earthquakes occurred on 13 January 2020. c. Distribution of earthquake magnitudes greater than 4.0 mb within a radius of 50 km from 1 November 2019 to 9 March 2020 around the Taal Volcano, data are taken from the USGS website. Soon after the volcanic eruption (red arrow), the frequency of mild magnitude earthquakes increased. We do not have access to the local earthquake catalog, so we cannot comment on small earthquakes; however, a few earthquakes of magnitude around 4.0 and larger have been observed (source: USGS).

Satellite data
The satellite data considered in the detailed analysis are given in Table 1. We used the MODIS aerosol optical depth (AOD) products (collection 6.1) [60] from the MODIS sensor through the NASA Giovanni portal (https://giovanni.gsfc.nasa.gov/giovanni/). For better temporal coverage, we have  Taal Volcano from 25 January 2000 -10 February 2020. The volcanic eruptions started on 12 January 2020, as indicated by the red arrow. (b) Distribution of earthquakes with magnitude greater than 4.0 mb (yellow dots) within a 50 km radius around the Taal volcano from 1 November 2019 to 9 March 2020. Yellow dots show the distribution of earthquake epicenters. A total of 35 earthquakes occurred on 12 January 2020, and afterward, 18 earthquakes occurred on 13 January 2020. (c) Distribution of earthquake magnitudes greater than 4.0 mb within a radius of 50 km from 1 November 2019 to 9 March 2020 around the Taal Volcano, data are taken from the USGS website. Soon after the volcanic eruption (red arrow), the frequency of mild magnitude earthquakes increased. We do not have access to the local earthquake catalog, so we cannot comment on small earthquakes; however, a few earthquakes of magnitude around 4.0 and larger have been observed (source: USGS).

Satellite data
The satellite data considered in the detailed analysis are given in Table 1. We used the MODIS aerosol optical depth (AOD) products (collection 6.1) [60] from the MODIS sensor through the NASA Giovanni portal (https://giovanni.gsfc.nasa.gov/giovanni/). For better temporal coverage, we have taken the mean of Terra and Aqua MODIS data for an individual day. Total Column Ozone (TCO) data observed by AIRS (Atmospheric Infrared Sounder) [61], onboard the Earth Observing System (EOS) polar-orbiting platform, was also used in the present work. We have considered an average of ascending (daytime) and descending (nighttime) modes data; ascending mode is when the satellite passes from south to north, whereas the descending mode is when the satellite passes from north to south over the Earth's surface. In ascending mode, the local pass time is around 1.30 p.m. (daytime), and in descending mode, local pass time is around 1.30 a.m. (nighttime) for the AIRS satellite. The AIRS daily L3 retrieved products-water vapor and relative humidity products-have been considered in the present work. These products have global coverage at a spatial resolution of 1.0 × 1.0 • [62]. Volcanoes are known to emit SO 2 in the atmosphere. We have considered the Column Amount of SO 2 (Planetary Boundary Layer) acquired by an Ozone Monitoring Instrument (OMI) [63], which measures the atmospheric aerosols properties and also differentiates between smoke aerosols, dust, and sulfates. OMI is one of the four instruments of the NASA Aura satellite mission, which passes the equator at 01:45 p.m. It observes the backscattered sunlight by various molecules in visible and UV bands with the help of a wide-field telescope. These telescopes relate to two imaging grating spectrometers, which help in the measurement of Ozone, NO 2 , SO 2 , and atmospheric aerosols. These satellite data are also downloaded through the NASA Giovanni portal. Sentinel-5P TROPOMI (TROPOspheric Monitoring Instrument) SO 2 , Ozone, and carbon monoxide (CO) datasets with high spatial, temporal, and spectral resolutions have been used in this study. The Sentinel-5P satellite was launched on 13 October 2017. The spatial resolution of TROPOMI SO 2 and Ozone data is 5.5 × 3.5 km. The available SO 2 and Ozone datasets were generated by the DOAS (Differential Optical Absorption Spectroscopy) method [64] and the direct-fitting algorithm [65], respectively. The TROPOMI CO dataset, with a spatial resolution of 5.5 × 7 km was retrieved with the SICOR (Shortwave Infrared Carbon Monoxide Retrieval) algorithm [66].

Ground observation data
We have used the Manila AERONET station (14.63 • N, 121.07 • E) data (67 km areal distance from the Taal volcano) (Figure 3). The AERONET is a ground-based network that uses sun and sky radiometers located throughout the world [67]. These stations help in the study of aerosols properties at local, regional, and global scales. The methodology of retrieval of aerosol parameters (aerosol optical depth-AOD, angstrom exponent-AE, the radius of the particles, and single scattering albedo-SSA, etc.) from AERONET stations has been discussed in detail by Dubovik and King [68] and Dubovik et al. [69]. In the present study, we have used AOD, AE, SSA, and the particle size distribution of aerosols coming from the source, Taal volcano. The data used is version 3 and level 1.5 data, as the quality-controlled level 2.0 data were not available at the time of analysis. These parameters are available through the web (https://aeronet.gsfc.nasa.gov/). Remote Sens. 2020, 12, 1026 7 of 23 7 checks are discussed in detail by Wong et al. [70]. The vertical resolution is different for different parameters, and the data sets are available with time intervals of 5 days [71]. We used data from three Bio-Argo floats (see Figure 3 for their locations): station [2902786] is in the direct path of the plume (according to the forward trajectory model shown in Figure 4), and station [2902784] is close to the region that is directly affected by volcanic emission. The station [2902753] is not located in the direct path of the plume coming from the Taal volcano. The data coming from the three stations are taken to analyze the vertical profile of the ocean variables from ~5 to 1000 m.

Modeling data
The NOAA air trajectory model-the Hybrid Single Particle Lagrangian Integrated Trajectory Model Version 4 (HYSPLIT4) for forward trajectories-was used to study the transport of ash coming from the Taal eruption. We carried out the HYSPILT forward trajectories calculation for a 150 h run and with a time interval of 6 h at 500, 5000, and 10,000 m heights, the trajectories show the transport of airmass from the Taal volcano eruptions during 12 -14 January 2020 ( Figure 4).
Air mass transport from a height of 500 m from the Taal volcano is seen over the ocean and coastal parts of Cambodia and Malaysia (Figure 4-i). The transport of airmass from the higher altitude affected the north-eastern oceanic regions of the Philippines, and on 14 January 2020, the airmass affected the southern Philippines from a 10 km altitude (Figure 4-ii,iii). The wind direction at the height of 500 m was in the north-east direction, which brings volcanic ash towards the north-west direction, whereas at 5000 and 10,000 m, the wind direction was in the south to south-westerly and dispersed volcanic ash in the north-east direction, which is clearly reflected from the forward trajectories ( Figure 4). During the Taal volcanic eruptions, ash was injected into the atmosphere up to a height of 14.5 km (https://so2.gsfc.nasa.gov/omps_2012_now.html#2020). The wind directions at different altitudes were observed from vector wind analysis using NOAA NCAR Reanalysis-II over the Philippines and close to the ground at a pressure level of 1000hPa. Near the surface, the wind was north-easterly, and at 600 hPa and 250 hPa pressure levels, the wind was westerly and southwesterly, which dispersed volcanic ash to the north-east to the Taal volcano ( Figure 4-ii, iii). The Argo Program is part of the Global Ocean Observing System. Argo floats are deployed in the oceans throughout the world. Argo floats data are used in this work to study the temporal changes in water temperature and salinity. Argo data are collected and made freely available by the International Argo Program, and different countries also run their Argo stations and contribute to the international efforts (www.argo.ucsd.edu;argo.jcommops.org). Data and automatic quality checks are discussed in detail by Wong et al. [70]. The vertical resolution is different for different parameters, and the data sets are available with time intervals of 5 days [71]. We used data from three Bio-Argo floats (see  The National Climatic Data Center (NCDC) of the US National Oceanic and Atmospheric Administration (NOAA) (www.ncdc.noaa.gov) provides access to various meteorological parameters for Manila station. These parameters are calculated by using modeling, assimilation techniques, and ground observations. The wind data has a 3-h temporal resolution for each day.
The wind rose diagrams at Kota Kinabalu, Sabah, Malaysia, and San Juan, Batangas, Philippines, were plotted using Weather Underground data (www.wunderground.com/history) ( Figure 5). The website provides real-time and historical data at various airports around the world. The wind data at Sabah, Malaysia, has half-hour temporal resolution, and at Batangas, Philippines, temporal resolution is one hour. The Manila wind rose diagram shown in Figure 5 is based on the wind data

Modeling data
The NOAA air trajectory model-the Hybrid Single Particle Lagrangian Integrated Trajectory Model Version 4 (HYSPLIT4) for forward trajectories-was used to study the transport of ash coming Remote Sens. 2020, 12, 1026 8 of 23 from the Taal eruption. We carried out the HYSPILT forward trajectories calculation for a 150 h run and with a time interval of 6 h at 500, 5000, and 10,000 m heights, the trajectories show the transport of airmass from the Taal volcano eruptions during 12 -14 January 2020 ( Figure 4).
Air mass transport from a height of 500 m from the Taal volcano is seen over the ocean and coastal parts of Cambodia and Malaysia (Figure 4i). The transport of airmass from the higher altitude affected the north-eastern oceanic regions of the Philippines, and on 14 January 2020, the airmass affected the southern Philippines from a 10 km altitude (Figure 4ii,iii). The wind direction at the height of 500 m was in the north-east direction, which brings volcanic ash towards the north-west direction, whereas at 5000 and 10,000 m, the wind direction was in the south to south-westerly and dispersed volcanic ash in the north-east direction, which is clearly reflected from the forward trajectories ( Figure 4). During the Taal volcanic eruptions, ash was injected into the atmosphere up to a height of 14.5 km (https://so2.gsfc.nasa.gov/omps_2012_now.html#2020). The wind directions at different altitudes were observed from vector wind analysis using NOAA NCAR Reanalysis-II over the Philippines and close to the ground at a pressure level of 1000hPa. Near the surface, the wind was north-easterly, and at 600 hPa and 250 hPa pressure levels, the wind was westerly and south-westerly, which dispersed volcanic ash to the north-east to the Taal volcano ( Figure 4ii,iii).
The National Climatic Data Center (NCDC) of the US National Oceanic and Atmospheric Administration (NOAA) (www.ncdc.noaa.gov) provides access to various meteorological parameters for Manila station. These parameters are calculated by using modeling, assimilation techniques, and ground observations. The wind data has a 3-h temporal resolution for each day.
The wind rose diagrams at Kota Kinabalu, Sabah, Malaysia, and San Juan, Batangas, Philippines, were plotted using Weather Underground data (www.wunderground.com/history) ( Figure 5). The website provides real-time and historical data at various airports around the world. The wind data at Sabah, Malaysia, has half-hour temporal resolution, and at Batangas, Philippines, temporal resolution is one hour. The Manila wind rose diagram shown in Figure 5 is based on the wind data taken from NOAA NCDC. The National Climatic Data Center (NCDC) of the US National Oceanic and Atmospheric Administration (NOAA) (www.ncdc.noaa.gov) provides access to various meteorological parameters for Manila station. These parameters are calculated by using modeling, assimilation techniques, and ground observations. The wind data has a 3-h temporal resolution for each day.
The wind rose diagrams at Kota Kinabalu, Sabah, Malaysia, and San Juan, Batangas, Philippines, were plotted using Weather Underground data (www.wunderground.com/history) ( Figure 5). The website provides real-time and historical data at various airports around the world. The wind data at Sabah, Malaysia, has half-hour temporal resolution, and at Batangas, Philippines, temporal resolution is one hour. The Manila wind rose diagram shown in Figure 5 is based on the wind data taken from NOAA NCDC.

Results
We have considered three areas (1×1°), Box 1 over Taal, Box 2 on the west side, and Box 3 on the east side ( Figure 3) to carry out a detailed analysis of satellite data for atmospheric and meteorological parameters for the period 31 December 2019 -31 January 2020. Spatial variations of SO2, Ozone, CO, sea surface temperature, and surface latent heat flux around the time of the Taal eruption have been analyzed.

Results
We have considered three areas (1 × 1 • ), Box 1 over Taal, Box 2 on the west side, and Box 3 on the east side ( Figure 3) to carry out a detailed analysis of satellite data for atmospheric and meteorological parameters for the period 31 December 2019 -31 January 2020. Spatial variations of SO 2 , Ozone, CO, sea surface temperature, and surface latent heat flux around the time of the Taal eruption have been analyzed.
Remote Sens. 2020, 12, 1026 9 of 23 Figure 6a shows the mean of Terra and Aqua MODIS AOD for better temporal resolution over three boxes for the periods 31 December -31 January 2020. The mean AOD for January 2020 is found to be 0.17, 0.12, and 0.18 for Boxes 1, 2, and 3, respectively. A sharp increase in the AOD value just after the volcanic eruption is observed over Boxes 1 and 2 as the shift of the airmass is seen towards the western and south-western regions as appeared from the forward trajectory of airmass from the Taal volcano (Figure 4i-iii)) and wind directions ( Figure 5). We have also analyzed the aerosol properties (AOD, AE, and Total Column Water-TCW) at the AERONET station in Manila using AERONET data (Figure 6b). The averaged AOD, AE, and TCW values during January 2020, respectively, are found to be 0.24, 1. Further, we have shown volume size distribution (there are some gaps in data on some days) of AOD at Manila AERONET station (Figure 7a). Before the eruption of the Taal, the presence of coarse particles was observed on 7 January 2020, which could be related to local dust mass (coarse particle size); however, on 16 and 19 January 2020, maxima peak was observed for the finer particles associated with the volcanic eruption. Higher AOD (1.27) and higher AE (1.55) were observed on 29 January 2020 (Figure 6b) along with a peak towards the finer particles at Manila station (Figure 7a), which was more prominent in comparison to the other days. The high volume of the fine particles was observed a few days after the volcanic eruptions depending upon the meteorological parameters. The coarser particles also reached Manila stations (67 km areal distance from Taal Volcano) on 21 January 2020. The concentrations of particles (fine and coarse) depend on the Taal eruption and meteorological conditions. It is difficult to estimate these unless one has high spatial and temporal ground and satellite data.

Properties of volcanic aerosols
The analysis of wind direction shows that westerly winds bring volcanic airmass to Manila and its surroundings, which leads to changes in aerosol properties ( Figure 5). Figure 7b shows the wavelength dependence of SSA during January 2020. On 7 January 2020, the mean SSA is close to 0.9, which shows the effect of mixed aerosols due to local sources of emissions. On 16 January 2020, higher SSA is observed at lower wavelengths and low SSA at longer wavelengths, which indicates the presence of finer particles (volcanic plume), and a low value of SSA shows the absorbing nature of aerosols (lower than 0.90). A similar pattern is also observed on 19 January 2020, with the higher SSA when compared to 16 January 2020, i.e., the aerosols are more reflecting in nature. During 22-28 January 2020, SSA is comparatively low and constant but on 29 January 2020, higher SSA value is observed again at a lower wavelength (lower values in infrared band), i.e., particles are finer, the average value of SSA is higher than 0.90, which means particles are reflecting in nature, which is characteristics of SO 2 . The changes in SSA clearly show emissions of volcanic ash, which was not regular after the volcanic event on 12 January 2020 and its transport (Figure 7b Figure 6a shows the mean of Terra and Aqua MODIS AOD for better temporal resolution over three boxes for the periods 31 December -31 January 2020. The mean AOD for January 2020 is found to be 0.17, 0.12, and 0.18 for Boxes 1, 2, and 3, respectively. A sharp increase in the AOD value just after the volcanic eruption is observed over Boxes 1 and 2 as the shift of the airmass is seen towards the western and south-western regions as appeared from the forward trajectory of airmass from the Taal volcano (Figure 4-i, ii, iii)) and wind directions ( Figure 5). We have also analyzed the aerosol properties (AOD, AE, and Total Column Water-TCW) at the AERONET station in Manila using AERONET data (Figure 6b). The averaged AOD, AE, and TCW values during January 2020, respectively, are found to be 0.24, 1.  Further, we have shown volume size distribution (there are some gaps in data on some days) of AOD at Manila AERONET station (Figure 7a). Before the eruption of the Taal, the presence of coarse particles was observed on 7 January 2020, which could be related to local dust mass (coarse particle size); however, on 16 and 19 January 2020, maxima peak was observed for the finer particles associated with the volcanic eruption. Higher AOD (1.27) and higher AE (1.55) were observed on 29 10 band), i.e., particles are finer, the average value of SSA is higher than 0.90, which means particles are reflecting in nature, which is characteristics of SO2. The changes in SSA clearly show emissions of volcanic ash, which was not regular after the volcanic event on 12 January 2020 and its transport (Figure 7b)

Emission of volcanic gases
Volcanic gases are important products of volcanic activities. We have analyzed SO2, Ozone, and CO data observed from satellites before and after the Taal volcano eruption.

SO2
SO2 emission from volcanoes is well known. Intense volcanic emission of SO2 and transport of volcanic ash was observed during and after the Taal volcano eruption (source-newsletter issued by PHIVOLCS) (https://volcano.si.edu/volcano.cfm?vn = 273070). The SO2 and volcanic ash were spread around the Taal volcano. We considered the total column of SO2 observed by OMI and TROPOMI with different spatial resolutions. These two kinds of data are more sensitive to SO2 at the upper troposphere and the lower stratosphere compared with those retrieving SO2 products based on thermal infrared measurements, such as IASI (Infrared Atmospheric Sounding Interferometer) and MODIS [64,72]. The OMI SO2 dataset is used for temporal analysis and TROPOMI for spatial variations. The average OMI SO2 is found to be 0.13, 0.27, and 0.23 DU (Dobson Unit) over Boxes 1, 2, and 3, respectively. For Box 1, SO2 data is unavailable between 13 and 19 January 2020. Over Boxes 2 and 3, a sharp rise in SO2 concentration is observed on 14 January 2020, with about 1.39 and 1.02 DU associated with the volcanic emission, which is higher than the mean value for January 2020 (

Emission of volcanic gases
Volcanic gases are important products of volcanic activities. We have analyzed SO 2 , Ozone, and CO data observed from satellites before and after the Taal volcano eruption. 4.2.1. SO 2 SO 2 emission from volcanoes is well known. Intense volcanic emission of SO 2 and transport of volcanic ash was observed during and after the Taal volcano eruption (source-newsletter issued by PHIVOLCS) (https://volcano.si.edu/volcano.cfm?vn=273070). The SO 2 and volcanic ash were spread around the Taal volcano. We considered the total column of SO 2 observed by OMI and TROPOMI with different spatial resolutions. These two kinds of data are more sensitive to SO 2 at the upper troposphere and the lower stratosphere compared with those retrieving SO 2 products based on thermal infrared measurements, such as IASI (Infrared Atmospheric Sounding Interferometer) and MODIS [64,72]. The OMI SO 2 dataset is used for temporal analysis and TROPOMI for spatial variations. The average OMI SO 2 is found to be 0.13, 0.27, and 0.23 DU (Dobson Unit) over Boxes 1, 2, and 3, respectively. For Box 1, SO2 data is unavailable between 13 and 19 January 2020. Over Boxes 2 and 3, a sharp rise in SO 2 concentration is observed on 14 January 2020, with about 1.39 and 1.02 DU associated with the volcanic emission, which is higher than the mean value for January 2020 ( The spatial distribution of enhanced SO 2 from Sentinel-5P TROPOMI is shown in Figure 9. The highest total vertical column of SO 2 appeared one day after the eruption and distributed along the northeast and the southwest. The strongest SO 2 emission (larger than 30 DU) on 13 January 2020 distributed over the Philippine Sea, northeast of the Taal volcano, which coincided with the forward trajectory of airmass at a higher altitude (Figure 4ii,iii) showing the sensitivity to the upper troposphere. Also, the obvious enhancement in SO 2 appeared in the surrounding region of the southwest of Taal. On 14 January, the enhanced SO 2 moved to the south-west and distributed over the ocean, with a lower value (less than 20 DU) compared to the preceding day. Enhanced SO 2 disappeared on 15 January 2020, from the Taal volcano, emissions of gases were intermittent, not continuous, which is supported from the variability in SO 2 concentrations. The earthquake occurrences were frequent on 12 and 13 January 2020, and afterward, few earthquakes occurred. The observed earthquakes were induced from volcanic eruptions, so obviously frequent earthquakes were observed on 12 and 13 January 2020, and afterward, the volcanic eruption was stopped. This observation clearly supports the observed low emissions of SO 2 after two days of eruptions. The spatial distribution of enhanced SO2 from Sentinel-5P TROPOMI is shown in Figure 9. The highest total vertical column of SO2 appeared one day after the eruption and distributed along the northeast and the southwest. The strongest SO2 emission (larger than 30 DU) on 13 January 2020 distributed over the Philippine Sea, northeast of the Taal volcano, which coincided with the forward trajectory of airmass at a higher altitude (Figure 4-ii, iii) showing the sensitivity to the upper troposphere. Also, the obvious enhancement in SO2 appeared in the surrounding region of the southwest of Taal. On 14 January, the enhanced SO2 moved to the south-west and distributed over the ocean, with a lower value (less than 20 DU) compared to the preceding day. Enhanced SO2 disappeared on 15 January 2020, from the Taal volcano, emissions of gases were intermittent, not continuous, which is supported from the variability in SO2 concentrations. The earthquake occurrences were frequent on 12 and 13 January 2020, and afterward, few earthquakes occurred. The observed earthquakes were induced from volcanic eruptions, so obviously frequent earthquakes were observed on 12 and 13 January 2020, and afterward, the volcanic eruption was stopped. This observation clearly supports the observed low emissions of SO2 after two days of eruptions.    Figure 8. Temporal variations of Total Column SO2 over Boxes 1 -3 using OMI measurements. A sharp rise in SO2 is observed over Boxes 2 and 3 on 14 January, and the volcanic eruptions started on 12 January 2020 (the black arrow points at the date of the volcanic eruption).
The spatial distribution of enhanced SO2 from Sentinel-5P TROPOMI is shown in Figure 9. The highest total vertical column of SO2 appeared one day after the eruption and distributed along the northeast and the southwest. The strongest SO2 emission (larger than 30 DU) on 13 January 2020 distributed over the Philippine Sea, northeast of the Taal volcano, which coincided with the forward trajectory of airmass at a higher altitude (Figure 4-ii, iii) showing the sensitivity to the upper troposphere. Also, the obvious enhancement in SO2 appeared in the surrounding region of the southwest of Taal. On 14 January, the enhanced SO2 moved to the south-west and distributed over the ocean, with a lower value (less than 20 DU) compared to the preceding day. Enhanced SO2 disappeared on 15 January 2020, from the Taal volcano, emissions of gases were intermittent, not continuous, which is supported from the variability in SO2 concentrations. The earthquake occurrences were frequent on 12 and 13 January 2020, and afterward, few earthquakes occurred. The observed earthquakes were induced from volcanic eruptions, so obviously frequent earthquakes were observed on 12 and 13 January 2020, and afterward, the volcanic eruption was stopped. This observation clearly supports the observed low emissions of SO2 after two days of eruptions.

Ozone
We have also analyzed the changes in total column ozone (TCO) over Box 1 to 3 around the Taal region.
The TCO observed by AIRS was low on 12 and 13 January 2020 over the three boxes ( Figure 3). Afterward, TCO was found to be enhanced (Figure 10a), corresponding to the increase in SO 2 due to the Taal eruption (Figures 8 and 10a). During the initial eruption, the higher SO 2 concentration affected the TCO (due to chemical reaction with atmospheric chlorine). Similar results were also observed with volcanic eruptions elsewhere [8,[73][74][75]. Variations of SO 2 concentrations over Box 1-3 are related to the amount of SO 2 emissions, thus, showing corresponding variations in TCO (Figure 10a). Variations of SO 2 over Box 1-3 ( Figure 8) depend on the wind directions, showing changes in TCO (Figure 10a). We also analyzed the spatial variations of TCO from TROPOMI Ozone data, and an obvious decrease has been observed over the Taal volcano region on 13 January 2020 (Figure 10b).   Figure 10c shows variations of SO 2 and TCO over Box 1 to 3 for the period 1-31 January 2020, and the downward black arrow shows the day of the Taal volcano eruption. Prior to the Taal eruption, a seasonal decline (winter season, January) in TCO is observed. After the Taal eruption on 12 January 2020, a peak in SO 2 injection in the planetary boundary layer is observed, which shows increasing values in TCO with strong variability corresponding to SO 2 emissions from the Taal volcano, which appear to decline as SO 2 emissions cease. Such emissions of SO 2 have a long term impact showing a decline in TCO (TCO appears to decline after 31 January 2020, which is also observed in the case of other volcanic eruptions) [8,[73][74][75].

CO
CO is another common volcanic degassing product [34], which could be determined by ground observation [76,77]. In 2012, it was first observed in the Eyjafjallajökull 2010 and Grímsvötn 2011 eruptions in Iceland using satellite data [39], which motivated us to carry out the analysis of Sentinel-5P TROPOMI CO data with a spatial resolution of 5.5 × 7 km. A slight increase in CO concentrations (Figure 11a) was observed over the Taal volcano region on 14 and 15 January 2020 (not enough data are available on 13 January over this region). AIRS CO mole fraction vertical profile over the Taal region (2 × 2 • ) also shows similar variations, though it has a low spatial resolution (Figure 11b). An increase in CO mole fraction appeared between 13 and 17 January 2020, soon after the eruption of the Taal volcano, especially at the pressure levels 500-1000 hPa.

13
the Taal eruption (Figures 8 and 10a). During the initial eruption, the higher SO2 concentration affected the TCO (due to chemical reaction with atmospheric chlorine). Similar results were also observed with volcanic eruptions elsewhere [8,[73][74][75]. Variations of SO2 concentrations over Box 1-3 are related to the amount of SO2 emissions, thus, showing corresponding variations in TCO ( Figure  10a). Variations of SO2 over Box 1-3 ( Figure 8) depend on the wind directions, showing changes in TCO (Figure 10a). We also analyzed the spatial variations of TCO from TROPOMI Ozone data, and an obvious decrease has been observed over the Taal volcano region on 13 January 2020 (Figure 10b). Figure 10c shows variations of SO2 and TCO over Box 1 to 3 for the period 1-31 January 2020, and the downward black arrow shows the day of the Taal volcano eruption. Prior to the Taal eruption, a seasonal decline (winter season, January) in TCO is observed. After the Taal eruption on 12 January 2020, a peak in SO2 injection in the planetary boundary layer is observed, which shows increasing values in TCO with strong variability corresponding to SO2 emissions from the Taal volcano, which appear to decline as SO2 emissions cease. Such emissions of SO2 have a long term impact showing a decline in TCO (TCO appears to decline after 31 January 2020, which is also observed in the case of other volcanic eruptions) [8,[73][74][75].

CO
CO is another common volcanic degassing product [34], which could be determined by ground observation [76,77]. In 2012, it was first observed in the Eyjafjallajökull 2010 and Grímsvötn 2011 eruptions in Iceland using satellite data [39], which motivated us to carry out the analysis of Sentinel-5P TROPOMI CO data with a spatial resolution of 5.5 × 7 km. A slight increase in CO concentrations (Figure 11a) was observed over the Taal volcano region on 14 and 15 January 2020 (not enough data are available on 13 January over this region). AIRS CO mole fraction vertical profile over the Taal region (2×2°) also shows similar variations, though it has a low spatial resolution (Figure 11b). An increase in CO mole fraction appeared between 13 and 17 January 2020, soon after the eruption of the Taal volcano, especially at the pressure levels 500 -1000 hPa.

Water vapor
Water vapor mixing ratio and relative humidity along vertical profiles ( Figure 12) over the Taal region (2×2°) observed by AIRS before and after the eruption of the Taal volcano have been considered. An obvious enhancement in both water vapor and relative humidity occurred on 12 and 13 January 2020 at the pressure levels 200-400 hPa compared to other days, which indicates the enhancements of the water mixing ratio and relative humidity in the upper troposphere. The enhanced water vapor could also cause an ozone decrease (Figure 10a,b) [78]. With the injection of hot gases from volcanic eruptions, the water vapor and relative humidity enhanced at pressure levels 850-1000 hPa on 13 January 2020, showing a pronounced increase compared with 12 January 2020.

Salinity and temperature
The vertical distributions of ocean salinity from three Argo stations have been analyzed ( Figure  13

Water vapor
Water vapor mixing ratio and relative humidity along vertical profiles ( Figure 12) over the Taal region (2×2 • ) observed by AIRS before and after the eruption of the Taal volcano have been considered. An obvious enhancement in both water vapor and relative humidity occurred on 12 and 13 January 2020 at the pressure levels 200-400 hPa compared to other days, which indicates the enhancements of the water mixing ratio and relative humidity in the upper troposphere. The enhanced water vapor could also cause an ozone decrease (Figure 10a,b) [78]. With the injection of hot gases from volcanic eruptions, the water vapor and relative humidity enhanced at pressure levels 850-1000 hPa on 13 January 2020, showing a pronounced increase compared with 12 January 2020.

Water vapor
Water vapor mixing ratio and relative humidity along vertical profiles ( Figure 12) over the Taal region (2×2°) observed by AIRS before and after the eruption of the Taal volcano have been considered. An obvious enhancement in both water vapor and relative humidity occurred on 12 and 13 January 2020 at the pressure levels 200-400 hPa compared to other days, which indicates the enhancements of the water mixing ratio and relative humidity in the upper troposphere. The enhanced water vapor could also cause an ozone decrease (Figure 10a,b) [78]. With the injection of hot gases from volcanic eruptions, the water vapor and relative humidity enhanced at pressure levels 850-1000 hPa on 13 January 2020, showing a pronounced increase compared with 12 January 2020.

Salinity and temperature
The vertical distributions of ocean salinity from three Argo stations have been analyzed ( Figure  13

Salinity and temperature
The vertical distributions of ocean salinity from three Argo stations have been analyzed (Figure 13 , salinity was higher on 7 January and later shows a decrease on the surface of the water, but the change is small. At station [2902784] (on the route of airmass transportation), the highest salinity close to the surface was found on 14 January 2020, and later on, a decrease in salinity at the depth levels between 0 and 20 m was observed. This decrease in ocean salinity is likely due to the intense deposition of thick ash, which was even observed on the roofs of houses (personal communication with Saroj Panda currently living in Manila and https://volcano.si.edu/volcano.cfm?vn=273070). For station [2902786], salinity was also higher close to the water surface on 13 January at similar depths, but at this station, the highest salinity was found on 27 January 2020. The salinity was found to be similar after a depth of 100 m at these two stations. water, but the change is small. At station [2902784] (on the route of airmass transportation), the highest salinity close to the surface was found on 14 January 2020, and later on, a decrease in salinity at the depth levels between 0 and 20 m was observed. This decrease in ocean salinity is likely due to the intense deposition of thick ash, which was even observed on the roofs of houses (personal communication with Saroj Panda currently living in Manila and https://volcano.si.edu/volcano.cfm?vn = 273070). For station [2902786], salinity was also higher close to the water surface on 13 January at similar depths, but at this station, the highest salinity was found on 27 January 2020. The salinity was found to be similar after a depth of 100 m at these two stations. We have also analyzed the vertical profiles of water temperature up to a 200 m (200 decibar pressure level) depth of the three Argo stations (Figure 14). At station [2902753], on 7 January 2020, the water temperature was higher up to the depth of 70 m, and the temperature was lowest at depths greater than 70 m. The temperature in deeper water at this station increased gradually until the end of the month (no data is available for 13 to 14 January 2020 for this station). At stations [2902784] and [2902786], a reduction in the shallow water temperature was observed on 14 and 13 January, respectively; later, a gradual rise in temperature was observed. An obvious variation in shallow water temperature was observed at station [2902784] because it is in the path of volcanic airmass transportation and was influenced by particle deposition. We have also analyzed the vertical profiles of water temperature up to a 200 m (200 decibar pressure level) depth of the three Argo stations (Figure 14). At station [2902753], on 7 January 2020, the water temperature was higher up to the depth of 70 m, and the temperature was lowest at depths greater than 70 m. The temperature in deeper water at this station increased gradually until the end of the month (no data is available for 13 to 14 January 2020 for this station). At stations [2902784] and [2902786], a reduction in the shallow water temperature was observed on 14 and 13 January, respectively; later, a gradual rise in temperature was observed. An obvious variation in shallow water temperature was observed at station [2902784] because it is in the path of volcanic airmass transportation and was influenced by particle deposition.  [2902786], salinity was also higher close to the water surface on 13 January at similar depths, but at this station, the highest salinity was found on 27 January 2020. The salinity was found to be similar after a depth of 100 m at these two stations. We have also analyzed the vertical profiles of water temperature up to a 200 m (200 decibar pressure level) depth of the three Argo stations (Figure 14). At station [2902753], on 7 January 2020, the water temperature was higher up to the depth of 70 m, and the temperature was lowest at depths greater than 70 m. The temperature in deeper water at this station increased gradually until the end of the month (no data is available for 13 to 14 January 2020 for this station). At stations [2902784] and [2902786], a reduction in the shallow water temperature was observed on 14 and 13 January, respectively; later, a gradual rise in temperature was observed. An obvious variation in shallow water temperature was observed at station [2902784] because it is in the path of volcanic airmass transportation and was influenced by particle deposition. Temporal variations of sea surface temperature (SST) were analyzed for a sub-selected region between 13 • N -15 • N latitudes and 120 • E -122 • E longitudes. For this purpose, Multi-scale Ultra-high Resolution (MUR) level-4 (L4) gap-free SST analysis data were obtained from NASA's JPL Physical Oceanography Distributed Active Archive Center (https://podaac.jpl.nasa.gov/Multi-scale_Ultra-high_ Resolution_MUR-SST). The temporal variation of SST was visualized here, for the period of 1 January to 16 February 2020, and additionally, with respect to climatological monthly average SST. The aim was to study any sharp changes in SST, relatively, and therefore the true value of SST is not relevant for this qualitative study. The MUR analysis product uses a variety of input SSTs and provides a grid resolution of~1 km, yielding about 21,900 points daily, for the sub-selected area of the study. Figure 15 shows the temporal variations of the SST (Y1 axis) and SST anomaly (Y2 axis). The mean SST anomaly shows a decrease in SST after the volcanic eruption until 16 January 2020, which is likely due to the fall of volcanic ashes, and after a few days, the SST increased. The mean SST shows a pronounced decline after January 2020, which is likely due to the spread of volcanic ashes over the ocean water surface, which is also evident from the observed decline in the ocean water temperature and salinity from Argo floats at the end of January (27)  Temporal variations of sea surface temperature (SST) were analyzed for a sub-selected region between 13 N -15 N latitudes and 120E -122 E longitudes. For this purpose, Multi-scale Ultra-high Resolution (MUR) level-4 (L4) gap-free SST analysis data were obtained from NASA's JPL Physical Oceanography Distributed Active Archive Center (https://podaac.jpl.nasa.gov/Multi-scale_Ultra-high_Resolution_MUR-SST). The temporal variation of SST was visualized here, for the period of 1 January to 16 February 2020, and additionally, with respect to climatological monthly average SST. The aim was to study any sharp changes in SST, relatively, and therefore the true value of SST is not relevant for this qualitative study. The MUR analysis product uses a variety of input SSTs and provides a grid resolution of ~1 km, yielding about 21,900 points daily, for the sub-selected area of the study. Figure 15 shows the temporal variations of the SST (Y1 axis) and SST anomaly (Y2 axis). The mean SST anomaly shows a decrease in SST after the volcanic eruption until 16 January 2020, which is likely due to the fall of volcanic ashes, and after a few days, the SST increased. The mean SST shows a pronounced decline after January 2020, which is likely due to the spread of volcanic ashes over the ocean water surface, which is also evident from the observed decline in the ocean water temperature and salinity from Argo floats at the end of January (27) 2020. Surface latent heat flux (SLHF) is an important parameter, reflecting the energy transportation between the ocean and the atmosphere. Higher SLHF is always observed at the ocean-land interface due to the high exchange of water vapor and heat with the atmosphere [79]. Considering the Taal volcano is surrounded by ocean, SLHF data are used to study the heat exchange over the surrounding atmosphere-ocean region around the time of the Taal volcano eruption. The SLHF dataset is obtained from the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis with a spatial resolution of 1.875° at longitude and an approximately 1.9° at latitude [80]. Figure 16 shows spatial distributions of daily SLHF around the Taal volcano for the period 8 -16 January 2020. An enhancement in SLHF is observed over the ocean, about 400 km south-west of the Taal volcano, between 12 and 14 January 2020. The highest enhancement appears on 13 January 2020, one day after the volcanic eruption. Surface latent heat flux (SLHF) is an important parameter, reflecting the energy transportation between the ocean and the atmosphere. Higher SLHF is always observed at the ocean-land interface due to the high exchange of water vapor and heat with the atmosphere [79]. Considering the Taal volcano is surrounded by ocean, SLHF data are used to study the heat exchange over the surrounding atmosphere-ocean region around the time of the Taal volcano eruption. The SLHF dataset is obtained from the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis with a spatial resolution of 1.875 • at longitude and an approximately 1.9 • at latitude [80]. Figure 16 shows spatial distributions of daily SLHF around the Taal volcano for the period 8 -16 January 2020. An enhancement in SLHF is observed over the ocean, about 400 km south-west of the Taal volcano, between 12 and 14 January 2020. The highest enhancement appears on 13 January 2020, one day after the volcanic eruption. Further, we have considered SLHF variations at different times 00, 06, 12, and 18 UTC daily. Figure 17 shows spatial variations of SLHF at 00, 06, 12, and 18 UTC for the periods 11 to 13 January 2020. An obvious variation occurred on the southwest of the Taal volcano, which is on the path of volcanic airmass transportation at a lower altitude (Figure 4-i). The increased SLHF is observed from 12 UTC, on 12 January 2020, six hours after the start of the eruption. The highest value appeared at 06 UTC on 13 January 2020. Temporal variations of the enhanced SLHF region have also been analyzed ( Figure 18). The distinct SLHF enhancement has been observed after the Taal volcano eruption, which was recovered on 15 January 2020 ( Figure 18). The highest value of 264.2 W/m 2 occurred at 06 UTC on 13 January 2020. We have also observed the high SLHF values in the northeast of the Taal volcano during this period, which could be attributed to the influence of Kuroshio flows during the winter season [81]. Further, we have considered SLHF variations at different times 00, 06, 12, and 18 UTC daily. Figure 17 shows spatial variations of SLHF at 00, 06, 12, and 18 UTC for the periods 11 to 13 January 2020. An obvious variation occurred on the southwest of the Taal volcano, which is on the path of volcanic airmass transportation at a lower altitude (Figure 4i). The increased SLHF is observed from 12 UTC, on 12 January 2020, six hours after the start of the eruption. The highest value appeared at 06 UTC on 13 January 2020. Temporal variations of the enhanced SLHF region have also been analyzed ( Figure 18). The distinct SLHF enhancement has been observed after the Taal volcano eruption, which was recovered on 15 January 2020 ( Figure 18). The highest value of 264.2 W/m 2 occurred at 06 UTC on 13 January 2020. We have also observed the high SLHF values in the north-east of the Taal volcano during this period, which could be attributed to the influence of Kuroshio flows during the winter season [81].

Discussion
The ash plume from the Taal volcanic eruption spreads in the surroundings of the Taal volcano, and the maximum ash plume spread is in the south-west, which is also evident from the wind rose diagram ( Figure 5). The volcanic eruptions triggered earthquakes, and an increase in the frequency of earthquakes (Figure 2a,b) was observed from the beginning of eruptions, with a few medium-sized earthquakes (magnitude greater than 4.0 mb) also observed (Figure 2c). The emissions of gases and volcanic ash began with the volcanic eruptions, which were dispersed around Taal guided by the wind directions near the surface and at the different altitudes. The volcanic ash reached up to 14.5 km altitude in the atmosphere, which was spread in the north-east directions from the Taal volcano [50] (https://so2.gsfc.nasa.gov/omps_2012_now.html#2020). The aerosol concentrations enhanced in the atmosphere over Taal and its surroundings. Higher values of AOD and high AE have been

Discussion
The ash plume from the Taal volcanic eruption spreads in the surroundings of the Taal volcano, and the maximum ash plume spread is in the south-west, which is also evident from the wind rose diagram ( Figure 5). The volcanic eruptions triggered earthquakes, and an increase in the frequency of earthquakes (Figure 2a,b) was observed from the beginning of eruptions, with a few medium-sized earthquakes (magnitude greater than 4.0 mb) also observed (Figure 2c). The emissions of gases and volcanic ash began with the volcanic eruptions, which were dispersed around Taal guided by the wind directions near the surface and at the different altitudes. The volcanic ash reached up to 14.5 km altitude in the atmosphere, which was spread in the north-east directions from the Taal volcano [50] (https://so2.gsfc.nasa.gov/omps_2012_now.html#2020). The aerosol concentrations enhanced in the atmosphere over Taal and its surroundings. Higher values of AOD and high AE have been observed at Manila under the influence of the western and south-west winds. Higher AOD shows an increase in atmospheric pollution affecting air quality, and larger values of AE show the presence of smoke/ashes ( Figure 6), which is also reflected from the increase in the volume size distribution of the small radius of particles (finer particles) (Figure 7a) after the eruption. A small increase in the volume of coarser particles was also observed from AERONET station at Manila. A decreasing trend of SSA with wavelength from the AERONET Manila station clearly shows the presence of volcanic ashes (Figure 7b). We observed the rapid decrease in ozone while SO 2 increased one day after the eruption of the Taal volcano (Figures 9 and 10a). That could be attributed to the discharging of significant emissions of reactive halogen that existed in volcanic plumes. The high correlation between SO 2 and halogen monoxides provided evidence for the volcanic origin of the reactive halogen species [82]. The self and cross-reactions of reactive halogen yield the destruction of ozone in the vicinity of the volcano (Figure 10a,b) [83]. The enhancement of water vapor in the upper troposphere has been observed after the volcanic eruption ( Figure 12). The concentration and distribution of water vapor and ozone are sensitive to both chemical processes, such as cloud microphysics and transport processes influencing the convection and stratosphere-troposphere exchange (STE) [84]. These processes influence the ozone concentrations and contribute to a warming of the tropopause, which allows higher water vapor concentrations to enter the stratosphere. Higher stratospheric water vapor coupled with stratospheric cooling induced by increases in atmospheric carbon dioxide can lead to increases in stratospheric ozone depletion. We observed an obvious variation of SLHF after the volcanic eruption, which could be related to the impact of volcanic ashes, but the mechanism still needs to be examined further.

Conclusion
We have analyzed the optical properties of volcanic aerosols, volcanic gas emission, and ocean parameters around the time of the eruption of the Taal volcano on 12 January 2020 using a combination of satellite and ground observations. Changes in aerosol optical depth (AOD) in the western and south-western regions after the Taal volcano eruption have been observed using MODIS AOD data and are likely to be associated with the transport of airmass as reflected by the forward trajectory analysis and wind directions. AOD, Angstrom Exponent (AE), aerosol size distribution (ASD), and single scattering albedo (SSA) acquired from the AERONET Manila station (67 km areal distance from the Taal volcano) indicated the presence of finer particles (volcanic ash plume). The results combined with satellite and ground observations suggest that the eruption of a volcano strongly influences the optical properties of aerosols. We have also observed pronounced variations in volcanic degassing based on different satellite observations with various spatial resolutions. An obvious enhancement in SO 2 appeared on 13 January 2020 in the surrounding region of the southwest of the Taal volcano. Also, a decline in ozone has been observed on the same day in the western region, which could be due to the chemical reaction of SO 2 and chlorine in the atmosphere. We have also observed enhanced CO, water vapor, and relative humidity in the troposphere. The observed that changes show evidence of a strong tropospheric-stratospheric exchange affecting the total column ozone (TCO). The unusual variations in salinity, sea temperature, and surface latent heat flux have also been found as a result of the westward airmass at a lower altitude from the Taal volcano over the ocean. Especially, some ocean parameters could be changed while volcanic ash reaches over the ocean and is deposited. Within a 20 km radius of the Taal volcano, thick ashes were deposited over the roofs of houses (PHIVOLCS, https://volcano.si.edu/volcano.cfm?vn=273070). The impact of the eruption was observed in the south-west direction from the volcanic ash at lower altitudes, whereas the changes were more prevalent in the north-east direction due to south-westerly winds at a higher altitude. The integrated approach combining multi-satellite observations, Argo measurements, AERONET data, and HYSPILT trajectories provides valuable information to study the changes in atmospheric and meteorological parameters, and such an approach may be used to study volcanic eruptions and to study the areal extent of the volcanic ash from volcanos.