Open AccessArticle
Characterization, Long-Range Transport and Source Identification of Carbonaceous Aerosols during Spring and Autumn Periods at a High Mountain Site in South China
Atmosphere 2016, 7(10), 122; doi:10.3390/atmos7100122 -
Abstract
PM10 (particulate matter) samples were collected at Mount Lu, a high elevation mountain site in south China (August and September of 2011; and March, April and May of 2012). Eight carbonaceous fractions of particles were analyzed to characterize the possible carbonaceous [...] Read more.
PM10 (particulate matter) samples were collected at Mount Lu, a high elevation mountain site in south China (August and September of 2011; and March, April and May of 2012). Eight carbonaceous fractions of particles were analyzed to characterize the possible carbonaceous emission sources. During the sampling events, daily average concentrations of PM10 at Mount Lu were 97.87 μg/m3 and 73.40 μg/m3 in spring and autumn, respectively. The observed mean organic carbon (OC) and element carbon (EC) concentrations during spring in PM10 were 10.58 μg/m3 and 2.58 μg/m3, respectively, and those in autumn were 6.89 μg/m3 and 2.40 μg/m3, respectively. Secondary organic carbon concentration was 4.77 μg/m3 and 2.93 μg/m3 on average, accounting for 28.0% and 31.0% of the total OC in spring and autumn, respectively. Relationships between carbonaceous species and results of principal component analysis showed that there were multiple sources contributing to the carbonaceous aerosols at the observation site. Through back trajectory analysis, it was found that air masses in autumn were mainly transported from the south of China, and these have the highest OC but lowest EC concentrations. Air masses in spring transported from northwest China bring 7.77 μg/m3 OC and 2.28 μg/m3 EC to the site, with lower levels coming from other sites. These air mass sources were featured by the effective carbon ratio (ECR). Full article
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Open AccessArticle
The Characteristics of Greenhouse Gas Emissions from Heavy-Duty Trucks in the Beijing-Tianjin-Hebei (BTH) Region in China
Atmosphere 2016, 7(9), 121; doi:10.3390/atmos7090121 -
Abstract
This paper aims to study the characteristics of greenhouse gas (GHG) emissions from heavy-duty trucks in the Beijing-Tianjin-Hebei (BTH) region, which is located in Northern China. The multiyear emissions of GHG (CO2, CH4 and N2O) from heavy-duty [...] Read more.
This paper aims to study the characteristics of greenhouse gas (GHG) emissions from heavy-duty trucks in the Beijing-Tianjin-Hebei (BTH) region, which is located in Northern China. The multiyear emissions of GHG (CO2, CH4 and N2O) from heavy-duty trucks fueled by diesel and natural gas during the period of 2006–2015 were compared and analyzed. The results show that the GHG emissions from heavy-duty trucks increase with time, which is consistent with the trend of the population growth. The total amount of carbon dioxide equivalence (CO2e) emissions in the BTH region was about 5.12 × 106 t in 2015. Among the three sub-regions, Hebei possesses the largest number of heavy-duty trucks due to the size of its heavy-duty industries. As a consequence, the GHG emissions are about 10 times compared to Beijing and Tianjin. Tractor trailers account for the major proportion of heavy-duty trucks and hence contribute to about 74% of GHG emissions. Diesel- and liquefied natural gas (LNG)-powered heavy-duty trucks can reduce GHG emissions more effectively under current national standard IV than can the previous standard. The widespread utilization of the alternative fuel of LNG to mitigate emissions must be accompanied with engine technology development in China. This study has provided new insight on management methods and the policy-making as regards trucks in terms of environmental demand. Full article
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Open AccessComment
Comment on Ernest et al. Programmable Thermal Dissociation of Reactive Gaseous Mercury, A Potential Approach to Chemical Speciation: Results from a Field Study. Atmosphere 2014, 5, 575–596
Atmosphere 2016, 7(9), 119; doi:10.3390/atmos7090119 -
Abstract The authors of this paper utilized a so-called “programmable thermal dissociation method” to monitor HgCl2 emitted from a coal-fired Florida combustion plant.[...] Full article
Open AccessReply
A Reply to Keith Schofield: Comment on Ernest et al. Programmable Thermal Dissociation of Reactive Gaseous Mercury, a Potential Approach to Chemical Speciation: Results from a Field Study. Atmosphere 2014, 5, 575–596
Atmosphere 2016, 7(9), 120; doi:10.3390/atmos7090120 -
Abstract Dr. Schofield [1] states that:[...] Full article
Open AccessArticle
A Case Study of a Heavy Rain over the Southeastern Tibetan Plateau
Atmosphere 2016, 7(9), 118; doi:10.3390/atmos7090118 -
Abstract
This research systematically studied heavy rain that occurred on 5 August 2014 over the southeastern Tibetan Plateau (31°N–35°N, 96°E–103°E) using orbital data from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR), the TRMM Multi-satellite Precipitation Analysis (TMPA) products, and the European [...] Read more.
This research systematically studied heavy rain that occurred on 5 August 2014 over the southeastern Tibetan Plateau (31°N–35°N, 96°E–103°E) using orbital data from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR), the TRMM Multi-satellite Precipitation Analysis (TMPA) products, and the European Centre for Medium-range Weather Forecast (ECMWF) Re-Analysis Interim reanalysis data (ERA-Interim). The data studied included spatial and temporal distributions of the precipitation; horizontal distributions and vertical structures of the precipitation system; convective storm top altitudes and types of rain; mean rainfall profiles; the influence of water vapor content before and after the rainfall; and the atmospheric circulation background. The results suggest that most precipitation on the Tibetan Plateau occurs in the southeast, and that the maximum near-surface precipitation rate for this event was more than 100 mm·h−1. The convection was so powerful that the convective storm top altitude surpassed 16 km. Furthermore, the water vapor content caused obvious changes in the upper troposphere and lower stratosphere (UTLS) area. The mean rainfall profile can be roughly divided into four layers and showed that the maximum rainfall rate appeared at about 5.5 km. Deep weak precipitation provided the largest contribution to the total precipitation, while the highest average precipitation rate was from deep strong convective precipitation. The atmospheric circulation situation is conducive to the formation of strong convective weather, and the terrain is also an external factor affecting precipitation for this event. Full article
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Open AccessReview
ELF Electromagnetic Waves from Lightning: The Schumann Resonances
Atmosphere 2016, 7(9), 116; doi:10.3390/atmos7090116 -
Abstract
Lightning produces electromagnetic fields and waves in all frequency ranges. In the extremely low frequency (ELF) range below 100 Hz, the global Schumann Resonances (SR) are excited at frequencies of 8 Hz, 14 Hz, 20 Hz, etc. This review is aimed at [...] Read more.
Lightning produces electromagnetic fields and waves in all frequency ranges. In the extremely low frequency (ELF) range below 100 Hz, the global Schumann Resonances (SR) are excited at frequencies of 8 Hz, 14 Hz, 20 Hz, etc. This review is aimed at the reader generally unfamiliar with the Schumann Resonances. First some historical context to SR research is given, followed by some theoretical background and examples of the extensive use of Schumann resonances in a variety of lightning-related studies in recent years, ranging from estimates of the spatial and temporal variations in global lighting activity, connections to global climate change, transient luminous events and extraterrestrial lightning. Both theoretical and experimental results of the global resonance phenomenon are presented. It is our hope that this review will increase the interest in SR among researchers previously unfamiliar with this phenomenon. Full article
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Open AccessArticle
Submicron Particle-Bound Mercury in University Teaching Rooms: A Summer Study from Two Polish Cities
Atmosphere 2016, 7(9), 117; doi:10.3390/atmos7090117 -
Abstract
The goal of the study was to determine the concentrations of submicron particulate matter (PM1) and of the mercury contained in it (Hgp) in the air in two teaching rooms in two Polish cities, Gliwice and Warsaw. The [...] Read more.
The goal of the study was to determine the concentrations of submicron particulate matter (PM1) and of the mercury contained in it (Hgp) in the air in two teaching rooms in two Polish cities, Gliwice and Warsaw. The levels of atmospheric particulate matter (PM) differ greatly between these two cities. The relations between the indoor (I) and outdoor (O) 24-h concentrations for each PM1 and Hgp were determined and, based on the conclusions, an attempt was made to identify the main sources of the indoor Hgp in both cities. During the whole measuring period (April–June 2015), in both Warsaw and Gliwice, the 24-h outdoor PM1 concentrations were slightly higher than the indoor ones (outdoor and indoor averages were equal to 19.3 µg m−3 and 14.5 µg·m−3, respectively, in Gliwice and to 13.2 µg·m−3 and 9.5 µg·m−3 in Warsaw). In Gliwice, the indoor concentrations of Hgp (2.4 pg·m−3 to 27.7 pg·m−3) were much higher than the outdoor ones (1.1 pg·m−3 to 6.1 pg·m−3); in Warsaw the average concentrations of Hgp were equal to 1.4 pg m−3 indoors and outdoors. The 24-h concentrations of Hgp and the 24-h I/O ratios for Hgp varied more intensely in Gliwice than in Warsaw throughout the whole measuring period. In Warsaw, the teaching room Hgp came mainly from the infiltration of atmospheric (outdoor) Hgp. In Gliwice, a part of the indoor Hgp infiltrated into the teaching room with the outdoor PM1 that most probably was then enriched with gaseous indoor Hg, what resulted in the relatively high indoor Hgp concentrations. Full article
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Open AccessArticle
Horizontal Electric Field in the Vicinity of Structures Hit by Lightning
Atmosphere 2016, 7(9), 115; doi:10.3390/atmos7090115 -
Abstract
The horizontal electric field at the ground surface in the vicinity of structures hit by lightning flashes is relevant to the safety of human beings and livestock; it determines the touch and step voltages around the structure. This paper uses an approximate [...] Read more.
The horizontal electric field at the ground surface in the vicinity of structures hit by lightning flashes is relevant to the safety of human beings and livestock; it determines the touch and step voltages around the structure. This paper uses an approximate analytical formula for calculating the horizontal electric field, which was adapted to take into account the effect of the structure foundation. The input for the calculation is the current waveform at the base of the structure, and the results agree well with those obtained by other authors using the finite-difference time-domain (FDTD) method. The approximate formula is applied to calculate touch and step voltages in the vicinity of a structure and the results show that the use of the direct current (DC) approximation to calculate touch and step voltages may lead to significant errors; especially for fast-rising currents and relatively good-conducting soils. This means that DC approximation could be used for positive first stroke and poor-conducting ground (ρ ≥ 1000 Ω∙m), but cannot be used for subsequent strokes and good-conducting ground (ρ ≤ 100 Ω∙m). Moreover, step voltages differ more from the DC approximation than the touch voltages. Full article
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Open AccessArticle
Temperature Change of Shanghai and Its Response to Global Warming and Urbanization
Atmosphere 2016, 7(9), 114; doi:10.3390/atmos7090114 -
Abstract
Shanghai is the biggest metropolis in China, and its local temperature change is affected not only by global warming but also by urbanization. Integrating the Mann-Kendall test, EMD (Empirical Mode Decomposition), Cross Wavelet Analysis and statistical methods, we studied the response of [...] Read more.
Shanghai is the biggest metropolis in China, and its local temperature change is affected not only by global warming but also by urbanization. Integrating the Mann-Kendall test, EMD (Empirical Mode Decomposition), Cross Wavelet Analysis and statistical methods, we studied the response of the local temperature change in Shanghai to global warming and urbanization. The results indicate that the local temperature at Shanghai present a significant warming trend under the background of global warming over the past 135 years. The local temperature at Shanghai displays 2-year, 6-year, 15-year, 23-year and 68-year periodic fluctuation, whereas global temperature shows 4-year, 9-year, 15-year, 23-year and 68-year cyclic variation. Although the two cycles are not exactly the same, they show some comparability. Urbanization facilitated the warming process of Shanghai. In the most recent 50 years, temperature difference between urban and suburban Shanghai has increased nearly 0.4 °C. The related indicators of urban development, such as population, built-up area, Gross Domestic Product (GDP), energy consumption and number of vehicles show significantly positive correlation with the temperature difference between urban and suburban area. In addition, the frequency of extreme high temperature has become higher, whereas the frequency of extreme low temperature has become lower over the most recent 55 years. Full article
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Open AccessArticle
Possible Impact of Climate Change on the Quality of Apples from the Major Producing Areas of China
Atmosphere 2016, 7(9), 113; doi:10.3390/atmos7090113 -
Abstract
Meteorological conditions are important environmental factors affecting apple quality. To understand the possible impact of climate change on the apple quality of the major producing areas in China and assess the quality of major apple species (e.g., Fuji, Ralls, and Golden Delicious), [...] Read more.
Meteorological conditions are important environmental factors affecting apple quality. To understand the possible impact of climate change on the apple quality of the major producing areas in China and assess the quality of major apple species (e.g., Fuji, Ralls, and Golden Delicious), we studied the variation trends and abrupt change characteristics of six major climate factors affecting seven physicochemical indices of apple quality across five apple regions, including the Loess Plateau, Bohai Bay, the Old Course of the Yellow River, Southwest Highlands, and Xinjiang, using statistical methods, meteorological indices, and the ArcGIS analysis tool based on the meteorological observational data from 1961 to 2013. The results show that the spatial and temporal distributions of annual average temperature, annual sunshine duration, average summer temperature, summer diurnal temperature range, and average summer relative humidity all significantly changed (except annual precipitation) and that abrupt changes occurred. The annual temperatures and average summer temperatures in the Loess Plateau apple region and the Liaoning producing region of Bohai Bay increased within optimal ranges. In addition, for high-value regions, the hours of sunshine decreased, helping to improve the fruit shape index, sugar-acid ratio, and vitamin C (VC) content. Relatively high temperatures continued to increase to high values which remained lower than the optimal upper limit; the diurnal temperature range continued to decrease; and the sunshine hours significantly decreased within the optimal range, which might have worsened fruit hardness, soluble sugar, and peel anthocyanin in the producing regions of Southwest Shandong of Bohai Bay, Southeast Hebei of the Old Course of the Yellow River, Northern Anhui, and Jiangsu. In the production regions of the Yun-Gui plateau in the Southwest highlands, increased summer temperature and the diurnal temperature range were both within the optimal ranges, which might have helped to reduce fruit hardness and increase soluble sugar content. However, continuously increased temperature and reduced sunshine might have worsened the apple shape index and fruit coloring. In the Xinjiang apple-producing region, the climate became warmer and more humid with reduced daily sunshine hours, which might have improved the exterior quality of apples and reduced fruit hardness. Thus, the climate changes over the last 50 years have positively affected the seven apple quality physicochemical properties in the Loess Plateau and Xinjiang, whereas the impacts on the different indices of apple quality in the other apple-producing regions are less coherent. In general, climate change has significantly affected the apple quality of the major production regions in China. Corresponding scientific measures are needed to assure high apple quality to increase the income of farmers in the future. Full article
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Open AccessArticle
Molecular Dications in Planetary Atmospheric Escape
Atmosphere 2016, 7(9), 112; doi:10.3390/atmos7090112 -
Abstract
Fundamental properties of multiply charged molecular ions, such as energetics, structure, stability, lifetime and fragmentation dynamics, are relevant to understand and model the behavior of gaseous plasmas as well as ionosphere and astrophysical environments. Experimental determinations of the Kinetic Energy Released (KER) [...] Read more.
Fundamental properties of multiply charged molecular ions, such as energetics, structure, stability, lifetime and fragmentation dynamics, are relevant to understand and model the behavior of gaseous plasmas as well as ionosphere and astrophysical environments. Experimental determinations of the Kinetic Energy Released (KER) for ions originating from dissociations reactions, induced by Coulomb explosion of doubly charged molecular ions (molecular dications) produced by double photoionization of CO2, N2O and C2H2 molecules of interest in planetary atmospheres, are reported. The KER measurement as a function of the ultraviolet (UV) photon energy in the range of 28–65 eV was extracted from the electron-ion-ion coincidence spectra obtained by using tunable synchrotron radiation coupled with ion imaging techniques at the ELETTRA Synchrotron Light Laboratory Trieste, Italy. These experiments, coupled with a computational analysis based on a Monte Carlo trajectory simulation, allow assessing the probability of escape for simple ionic species in the upper atmosphere of Mars, Venus and Titan. The measured KER in the case of H+, C+, CH+, CH2+, N+, O+, CO+, N2+ and NO+ fragment ions range between 1.0 and 5.5 eV, being large enough to allow these ionic species to participate in the atmospheric escape from such planets into space. In the case of Mars, we suggest a possible explanation for the observed behavior of the O+ and CO22+ ion density profiles. Full article
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Open AccessArticle
Effect of the Aerosol Type Selection for the Retrieval of Shortwave Ground Net Radiation: Case Study Using Landsat 8 Data
Atmosphere 2016, 7(9), 111; doi:10.3390/atmos7090111 -
Abstract
This paper discusses the aerosol radiative effects involved in the accuracy of shortwave net radiation, Rn.sw, with sw (400–900) nm, retrieved by the Operational Land Imager (OLI), the new generation sensor of the Landsat mission. [...] Read more.
This paper discusses the aerosol radiative effects involved in the accuracy of shortwave net radiation, Rn.sw, with sw (400–900) nm, retrieved by the Operational Land Imager (OLI), the new generation sensor of the Landsat mission. Net radiation is a key parameter for the energy exchange between the land and atmosphere; thus, Rn.sw retrieval from space is under investigation by exploiting the increased spatial resolution of the visible and near-infrared OLI data. We adopted the latest version of the Second Simulation of a Satellite Signal in the Solar Spectrum (6SV) atmospheric radiative transfer model implemented in the atmospheric correction algorithm (OLI Atmospherically-Corrected Reflectance Imagery (OLI@CRI)) developed specifically for OLI data. The values of Rn.sw were obtained by varying the microphysical properties of the aerosol during the OLI@CRI retrieval of both the OLI surface reflectance, ρpxloli, and the incoming solar irradiance at the surface. The analysis of the aerosol effects on the Rn.sw was carried out on a spectrally-homogeneous desert area located in the southwestern Nile Delta. The results reveal that the Rn.sw available for energy exchange between the land and atmosphere reduces the accuracy (NRMSE ≃ 14%) when the local aerosol microphysical properties are not considered during the processing of space data. Consequently, these findings suggest that the aerosol type should be considered for variables retrieved by satellite observations concerning the energy exchange in the natural ecosystems, such as Photosynthetically-Active Radiation (PAR). This will also improve the accuracy of land monitoring and of solar energy for power generation when space data are used. Full article
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Open AccessArticle
Importance of Gaseous Elemental Mercury Fluxes in Western Maryland
Atmosphere 2016, 7(9), 110; doi:10.3390/atmos7090110 -
Abstract
The purpose of this study was to increase our understanding of the gaseous elemental mercury (GEM, Hg°) fluxes between the atmosphere and soils. Moreover, we wanted to quantify the annual GEM flux, identify the controls, and compare the GEM flux to annual [...] Read more.
The purpose of this study was to increase our understanding of the gaseous elemental mercury (GEM, Hg°) fluxes between the atmosphere and soils. Moreover, we wanted to quantify the annual GEM flux, identify the controls, and compare the GEM flux to annual rates of gaseous oxidized mercury (GOM) dry deposition and wet deposition of total mercury. We measured GEM fluxes using the modified Bowen ratio (MBR) technique from 6 July 2009 to 6 July 2010 in western Maryland. The annual hourly mean (±std. dev.) GEM flux was −0.63 ± 31.0 ng·m−2·h−1. Hourly mean GEM fluxes were not strongly correlated with atmospheric trace gases, aerosols, or meteorology. However, hourly mean GEM emissions (15.3 ± 27.9 ng·m−2·h−1) and deposition (−14.6 ± 26.6 ng·m−2·h−1) were correlated with ultraviolet-B radiation (UV-B), wind speed (WS), ozone (O3), and relative humidity (RH). The annual net GEM flux was −3.33 µg· m−2·year−1 and was similar to the annual dry deposition rate of GOM (2.5 to 3.2 µg·m−2·year−1), and 40% less than the annual mean wet deposition (8 µg·m−2·year−1) of total mercury. Thus, dry deposition of GEM accounted for approximately 25% of the total annual mercury deposition (~14 ug·m−2·year−1) measured at our study site. Full article
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Open AccessArticle
Intercomparison of Carbon Dioxide Products Retrieved from GOSAT Short-Wavelength Infrared Spectra for Three Years (2010–2012)
Atmosphere 2016, 7(9), 109; doi:10.3390/atmos7090109 -
Abstract
This paper presents the comparison of two CO2 datasets from the National Institute for Environmental Studies (NIES) of Japan and the Atmospheric CO2 Observations from Space (ACOS) of NASA for three years (2010 to 2012). Both CO2 datasets are [...] Read more.
This paper presents the comparison of two CO2 datasets from the National Institute for Environmental Studies (NIES) of Japan and the Atmospheric CO2 Observations from Space (ACOS) of NASA for three years (2010 to 2012). Both CO2 datasets are retrieved from the Greenhouse gases Observing SATellite (GOSAT) short-wavelength infrared spectra over High gain surface land. In this three-year period, the yield of the NIES CO2 column averaged dry air mole fractions (XCO2) is about 71% of ACOS retrievals. The overall bias is 0.21 ± 1.85 ppm and −0.69 ± 2.13 ppm for ACOS and NIES XCO2, respectively, when compared with ground-based Fourier Transform Spectrometer (FTS) observations from twelve Total Carbon Column Observing Network (TCCON) sites. The differences in XCO2 three-year means and seasonal means are within about 1 to 2 ppm. Strong consistency is obtained for the ACOS and NIES XCO2 monthly averages time series over different regions, with the greatest mean difference of ACOS to NIES monthly means over China (1.43 ± 0.60 ppm) and the least over Brazil (−0.03 ± 0.64 ppm). The intercomparison between the two XCO2 datasets indicates that the ACOS XCO2 is globally higher than NIES by about 1 ppm and has smaller bias and better consistency than NIES data. Full article
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Open AccessArticle
Evaluating Summer-Time Ozone Enhancement Events in the Southeast United States
Atmosphere 2016, 7(8), 108; doi:10.3390/atmos7080108 -
Abstract
This study evaluates source attribution of ozone (O3) in the southeast United States (US) within O3 lamina observed by the University of Alabama in Huntsville (UAH) Tropospheric Ozone Lidar Network (TOLNet) system during June 2013. This research applies surface-level [...] Read more.
This study evaluates source attribution of ozone (O3) in the southeast United States (US) within O3 lamina observed by the University of Alabama in Huntsville (UAH) Tropospheric Ozone Lidar Network (TOLNet) system during June 2013. This research applies surface-level and airborne in situ data and chemical transport model simulations (GEOS-Chem) in order to quantify the impact of North American anthropogenic emissions, wildfires, lightning NOx, and long-range/stratospheric transport on the observed O3 lamina. During the summer of 2013, two anomalous O3 layers were observed: (1) a nocturnal near-surface enhancement and (2) a late evening elevated (3–6 km above ground level) O3 lamina. A “brute force” zeroing method was applied to quantify the impact of individual emission sources and transport pathways on the vertical distribution of O3 during the two observed lamina. Results show that the nocturnal O3 enhancement on 12 June 2013 below 3 km was primarily due to wildfire emissions and the fact that daily maximum anthropogenic emission contributions occurred during these night-time hours. During the second case study it was predicted that above average contributions from long-range/stratospheric transport was largely contributing to the O3 lamina observed between 3 and 6 km on 29 June 2013. Other models, remote-sensing observations, and ground-based/airborne in situ data agree with the source attribution predicted by GEOS-Chem simulations. Overall, this study demonstrates the dynamic atmospheric chemistry occurring in the southeast US and displays the various emission sources and transport processes impacting O3 enhancements at different vertical levels of the troposphere. Full article
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Open AccessArticle
Effects of Plastic Mulch on Soil Heat Flux and Energy Balance in a Cotton Field in Northwest China
Atmosphere 2016, 7(8), 107; doi:10.3390/atmos7080107 -
Abstract
Surface energy balance (SEB) is a basic principle for all of the atmospheric circulation models, and surface soil heat flux (G0) is an important component of energy balance. Plastic mulch is widely used in arid regions and alters land [...] Read more.
Surface energy balance (SEB) is a basic principle for all of the atmospheric circulation models, and surface soil heat flux (G0) is an important component of energy balance. Plastic mulch is widely used in arid regions and alters land surface processes. In this study, hourly/daily G0 and SEB over a mulched cotton field were analyzed in Northwest China. The net radiation beneath the mulch was simulated using transmitted down short-wave and down long-wave radiation through the mulch and up short-wave and up long-wave radiation from the soil beneath mulch. The results show that: (1) on the hourly time scale, G0 in mulched soil is much smaller than that in non-mulched soil, day and night. This implies that mulch prevents energy going into the soil during the daytime and reduces soil heat loss at night. On the daily time scale, G0 is similar in mulched and non-mulched soil. (2) During the seedling emergence period when the cotton is small, the energy balance closure over mulched soil (0.79) is slightly smaller than that over non-mulched soil (0.81). (3) Comparing to soil temperature in non-mulched soil, there’s a time offset on soil temperature in mulched soil at the same depth, which will bring a hysteresis on G0 and SEB. Full article
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Open AccessArticle
An Improved Iterative Fitting Method to Estimate Nocturnal Residual Layer Height
Atmosphere 2016, 7(8), 106; doi:10.3390/atmos7080106 -
Abstract
The planetary boundary layer (PBL) is an atmospheric region near the Earth’s surface. It is significant for weather forecasting and for the study of air quality and climate. In this study, the top of nocturnal residual layers—which are what remain of the [...] Read more.
The planetary boundary layer (PBL) is an atmospheric region near the Earth’s surface. It is significant for weather forecasting and for the study of air quality and climate. In this study, the top of nocturnal residual layers—which are what remain of the daytime mixing layer—are estimated by an elastic backscatter Lidar in Wuhan (30.5°N, 114.4°E), a city in Central China. The ideal profile fitting method is widely applied to determine the nocturnal residual layer height (RLH) from Lidar data. However, the method is seriously affected by an optical thick layer. Thus, we propose an improved iterative fitting method to eliminate the optical thick layer effect on RLH detection using Lidar. Two typical case studies observed by elastic Lidar are presented to demonstrate the theory and advantage of the proposed method. Results of case analysis indicate that the improved method is more practical and precise than profile-fitting, gradient, and wavelet covariance transform method in terms of nocturnal RLH evaluation under low cloud conditions. Long-term observations of RLH performed with ideal profile fitting and improved methods were carried out in Wuhan from 28 May 2011 to 17 June 2016. Comparisons of Lidar-derived RLHs with the two types of methods verify that the improved solution is practical. Statistical analysis of a six-year Lidar signal was conducted to reveal the monthly average values of nocturnal RLH in Wuhan. A clear RLH monthly cycle with a maximum mean height of about 1.8 km above ground level was observed in August, and a minimum height of about 0.7 km was observed in January. The variation in monthly mean RLH displays an obvious quarterly dependence, which coincides with the annual variation in local surface temperature. Full article
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Open AccessArticle
Seasonal Variation of Nitrate Concentration and Its Direct Radiative Forcing over East Asia
Atmosphere 2016, 7(8), 105; doi:10.3390/atmos7080105 -
Abstract
This study investigated the seasonal variation of nitrate concentration and its radiative forcing over East Asia by using an online-coupled regional climate model. Comparison with a series of in-situ observations from Acid Deposition Monitoring Network in East Asia (EANET) and China demonstrated [...] Read more.
This study investigated the seasonal variation of nitrate concentration and its radiative forcing over East Asia by using an online-coupled regional climate model. Comparison with a series of in-situ observations from Acid Deposition Monitoring Network in East Asia (EANET) and China demonstrated a good skill of the model in reproducing the magnitude and seasonality of nitrate concentration across East Asia. It was found that nitrate concentration in Beijing and Tianjin exhibited the maximum in summer and the minimum in winter possibly due to stronger chemical oxidation and regional transport effect of larger emissions from the north China Plain in summer, whereas in most areas of East Asia, nitrate concentration was higher in winter and lower in summer, consistent with the seasonality of NOx emission. Surface nitrate concentration was higher over the lower reaches of the Yellow River, followed by the middle to lower reaches of the Yangtze River and portions of south China, and lower in Korean Peninsula and Japan. The annual mean surface nitrate concentration was predicted to be 2.9 μg·m−3 for East Asia and 8.5 μg·m−3 for east China. All-sky direct radiative forcing (DRF) due to nitrate at the top of the atmosphere (TOA) exhibited the largest forcing up to −7 W·m−2 over the lower reaches of the Yellow River, and lower forcing of ~−2 W·m−2 in the Korean Peninsula and Japan. Clear-sky DRF by nitrate reached the maximum in spring and the minimum in summer over both East Asia and east China, whereas DRF under all-sky condition showed its maximum in autumn, associated with seasonalities of nitrate column burden, relative humidity, and cloud effect. Annual mean all-sky DRFs at TOA were estimated to be −1.7 W·m−2 and −3.7 W·m−2 over East Asia and east China, respectively, significantly larger than global annual mean, suggesting the important role of nitrate aerosol in environment and climate change over East Asia. Full article
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Open AccessArticle
Retention of Atmospheric Particles by Local Plant Leaves in the Mount Wutai Scenic Area, China
Atmosphere 2016, 7(8), 104; doi:10.3390/atmos7080104 -
Abstract
To evaluate the characteristics of atmospheric particle retention by plant leaves during the tourism season in Buddhism-based scenic areas, plants distributed in the core area of the Mount Wutai scenic area were selected for study: Populus davidiana (Po. davidiana), Rosa[...] Read more.
To evaluate the characteristics of atmospheric particle retention by plant leaves during the tourism season in Buddhism-based scenic areas, plants distributed in the core area of the Mount Wutai scenic area were selected for study: Populus davidiana (Po. davidiana), Rosa hugonis Hemsl. (R. hugonis), Betula platyphylla Suk. (B. platyphylla), Rosa xanthina Lindl. (R. xanthina), Periploca sepium Bunge (Pe. sepium), Spiraea salicifolia L. (S. salicifolia), Vitex negundo var. Heterophylla (V. negundo var. heterophylla) and Pinus tabuliformis Carrière (Pi. tabuliformis). Before rain, the atmospheric suspended particle-retaining weight of the plant leaves varied in the range of 6.95 ± 1.55 (Pi. tabuliformis) to 38.60 ± 18.32 mg/cm2 (Po. davidiana); the light shaded areas caused by particles on leaves were in the range of 7.25 ± 0.04 (Pi. tabuliformis) to 126.50 ± 6.66 cm2/leaf (Po. davidiana); and the atmospheric particle-retaining horizontal density of leaves varied in the range of 110 ± 2 (Pi. tabuliformis) to 255 ± 11 per cm2 (Po. davidiana). After rain, the atmospheric suspended particle-retaining quality of plant leaves varied in the range of 0.65 ± 0.23 (Pi. tabuliformis) to 3.50 ± 1.83 mg/cm2 (Po. davidiana); the light shaded areas by particles on leaves were in the range of 4.26 ± 0.02 (Pi. tabuliformis) to 45.96 ± 2.42 cm2/leaf (Po. davidiana); and the atmospheric particle-retaining horizontal density of leaves was in the range of 97 ± 2 (Pi. tabuliformis) to 147 ± 7 per cm2 (Po. davidiana). The broad-leaved plants, particularly Po. davidiana, R. hugonis and B. platyphylla, were appropriate species for purification of atmospheric particles. Plants with lower dust-retention abilities than the above three species (e.g., R. xanthina, Pe. sepium, S. salicifolia and V. negundo var. heterophylla) could be alternative plants for purification. However, the needle-leaved plant Pi. tabuliformis was not recommended as a tree species for purification of atmospheric particles in the core area of the Mount Wutai scenic area. Full article
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Open AccessArticle
GNSS Measurement of Rain Rate by Polarimetric Phase Shift: Theoretical Analysis
Atmosphere 2016, 7(8), 101; doi:10.3390/atmos7080101 -
Abstract
In this paper, a novel method for rain rate estimation is researched by polarimetric phase shift of the Global Navigation Satellite System (GNSS). The physical process of GNSS signals propagating through rain-filled medium is investigated, by which the cause of polarimetric phase [...] Read more.
In this paper, a novel method for rain rate estimation is researched by polarimetric phase shift of the Global Navigation Satellite System (GNSS). The physical process of GNSS signals propagating through rain-filled medium is investigated, by which the cause of polarimetric phase shift is explored. Then, a theoretical model between polarimetric phase shift Δϕ and rain rate R is established and simulated, which is based on the oblate spheroid raindrop model, four different popular raindrop size distribution models and raindrop canting angle distribution across the Space-Earth rain path. Additionally, effects of raindrop size distribution, rain path length, raindrop canting angle and temperature on the Δϕ-R relation are discussed systematically. Other factors in the slant path such as ice crystals, melting particles and ionosphere are also researched preliminarily. The results show that polarimetric phase shift of GNSS signals, which has a strong correlation with rain rate, can be used to estimate the rain rate, and these influencing factors, raindrop size distribution, rain path length, raindrop canting angle and temperature, are quite important in the process of rain rate measurement. It can be also found that the effect of ice crystals can be negligible, while that of melting particles should be considered, and though ionosphere effects are not obvious, the ionospheric anomalies cannot be neglected in future experiments. This method has potential applications in real-time, continuous, extreme precipitation reconnaissance and numerical weather prediction. Full article
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