Air Quality and Atmospheric Emissions from the Operation of the Main Mexican Port in the Gulf of Mexico from 2019 to 2020

Abstract

Pollutant emissions into the atmosphere derived from port activities can be transported to surrounding regions and cities depending on wind speed and direction, having an impact on air quality. In this research, emissions of atmospheric pollutants (NOx, CO, NMHCs, CO₂, SO₂, TSP, PM_2.5 and PM₁₀) were estimated for: tanks, container, roll-on/roll-off (RO-RO), bulk carriers and general cargo ships, using emission factors in the hoteling and maneuvering stage in the port area of Veracruz, Mexico, during 2019 and 2020 despite the suspension period of activities due to the SARS-CoV-2/COVID-19 pandemic. Among the total estimated emissions, CO₂ presented the highest values for 2019 (31,177 kg/year) and 2020 (29,003 kg/year), whereas CH₄ presented the lowest values with 0.294 kg/year for 2019 and 0.273 kg/year for 2020. The highest estimated emissions for CO₂, NOx and SO₂ occurred in the maneuvering stage in 2019 for bulk carriers, tanks and container ships. Likewise, the highest estimated emissions were during the hoteling stage of the container ships in 2020. This study will provide an updated ship emissions inventory for the Gulf of Mexico region where the Port of Veracruz is located. In addition, SO₂ and PM_2.5 measurements were performed from October 2019 to December 2020. PM_2.5 concentrations exceeded the Mexican Ambient Air Quality Standard (MAAQS) value of 45 µg m⁻³ for the 24-h average concentration several times, on the opposite, SO₂ exhibited concentrations up to 20 times lower than the 24-h MAAQS value of 40 ppb. Results showed that pollutant emissions in the port of Veracruz exhibited a seasonal variability, modifying their dispersion and the possible effects. Our main conclusion is that current port area is the major source of pollutant emissions (SO₂ and PM_2.5) throughout the year, whereas the expansion area of the port of Veracruz does not represent still a significant rise of pollutant emissions, but it is expected that the growth of port activity will directly increase the concentrations of pollutants emitted.

1. Introduction

Several studies have reported that pollutant emissions from ships and port areas modify the air quality of the areas where they are located as well as other regions or nearby cities due to the emissions transport, and are important contributors to global air pollution [1,2,3,4] The increase in these emissions is directly related to international port activity, in which the use of larger vessels, high capacity and consequently greater fuel consumption, is intended to satisfy commercial needs [5,6,7,8].

Emissions from ships are dominated by nitrogen oxides (NOx), sulfur dioxide (SO₂), carbon monoxide (CO), carbon dioxide (CO₂), volatile organic compounds (COV), black carbon (BC) and particulate matter (PM). Several studies have been carried out to develop emissions inventories applying emission factors (EF), to report the amount of total atmospheric pollutants emitted by different types of ships (container ships, tankers, for RO-RO rolling cargo, ships for petroleum derivatives and general cargo) in a given period of time and the percentage contribution of each pollutant [9,10].

Currently, several calculation methods are available for estimating emissions from ships, which are classified into two groups [7]. On the one hand, “top-down” approach, in which very specific data such as fuel consumption of ships are used as well as emission factors based on the chemical properties of the fuel. On the other hand, the methods with a “bottom-up” approach employ an Automatic Identification System (AIS) for its accuracy in obtaining data, in addition to detailed information on the different ships [11] that dock in the port, including: ship speed, ship activity (maneuvering, cruising or hoteling), route, engine workload, location [12,13,14], among others. Emission estimation is the method commonly adopted by various researchers [15,16,17,18,19] where different assumptions are used [20].

Among the results reported, several authors using EF agree that the greatest contributions, considering the different types of ships, come from the so-called container ships followed by the RO-RO [12,21,22,23]. Nevertheless, the type and amount of fuel used by ships, the activity performed (cruise, maneuvering or hoteling) and the speed of the ships are directly related to the total emissions in a port region [1,24].

Air quality monitoring is very important to protect the population health; it has been documented that the cities close to the port and the port itself, depict a greater contribution to environmental pollution [23,25,26,27,28,29,30]. For instance, ships in operation produce an estimated 1.2 to 1.6 million tons of PM₁₀ per year and represent an important source of air pollution for coastal communities [31,32,33]. Several cities have proposed strategies to reduce the production of pollutants from port traffic [34,35,36,37].

In Mexico, the development of emission inventories and the evaluation of the impacts of port-related and good movements emission on local and regional air quality are activities that are outside the focus of environmental authorities and are poorly studied [38,39,40]. A recent study shows that the port of Veracruz is one of the ports with the highest atmospheric emissions from ships [41], so the participation and contribution of multidisciplinary groups from research institutions should be considered, Universidad Autónoma Metropolitana, Unidad Azcapotzalco (UAM-AZC), Instituto de Ciencias de la Atmósfera y Cambio Climático de la Universidad Nacional Autónoma de México (ICAyCC-UNAM) to evaluate air quality and produce a clearer trend for the short and long terms.

Therefore, the main aim of this research was the Veracruz port air quality assessment from October 2019 to December 2020, considering the emission estimations from ships during maneuvering and hoteling activities, the development of an emissions inventory and the diagnostic analysis of the area through application of meteorological measurements in order to analyze the seasonal and temporal variation of pollutants at the study site. This research begins in March 2020 when activities were reduced and even suspended in different areas around the world due to the COVID-19 pandemic period, resulting in the closure of markets. Although different studies were developed during the pandemic period, few refer to the maritime activity that was affected between the months of January and April of the same year; presenting a recovery between the months of May and June [42].

2. Materials and Methods

2.1. Study Area

Mexico is currently connected with more than 300 ports of the world through its port system. Figure 1 shows the Port of Veracruz with more than 170 foreign shipping lines.

The Integral Administration of the Veracruz Port (APIVER) area is surrounded by the metropolitan area of Veracruz City and some important tourist attractions such as the San Juan de Ulúa Fortress. Due to its strategic location the Port of Veracruz is one of the most important commercial ports in the country, with many commercial routes established to the Atlantic, and an expansion project in the North began since 2014. The operations carried out in the Port of Veracruz have been coordinated and supervised by APIVER; the associated activities with this expansion project include the construction and operation of new terminals, trebling the current infrastructure capacity of the Port Area, as well as the loading and unloading of assorted ships, storage of merchandise, ships repair, administrative services, and port management. For these activities, the Port Area is structured with the participation of assignees, service providers, carriers, customs agencies, port authorities, and different institutions that also participate.

The port has 8 docks distributed over 3.5 km in length, 71,325 m² of covered storage, 18,707 m² of storage yards and 116 ha of north expansion for the port development. During the realization of the study they had 18 docking positions for commercial cargo handling. Maritime traffic in the Port of Veracruz has gradually increased due to the surge in the tonnage of import and export merchandise handled in the country. During 2019, a total cargo movement of 28,273.284 tons was registered and 1861 ships were attended (tanks 362, bulk carriers 331, general cargo 264, RO-RO 297 and container carrier 627); while in 2020 a total cargo movement of 26,199.305 tons was registered for 1374 ships (tanks 282, bulk carrier 273, general cargo 181, RO-RO 159, container carrier 478), probably due to the pandemic, this was 7.3% lower than in 2019.

2.2. Estimations and Measurements

To determine the air quality impacts due to emissions to the atmosphere from ships, EF were used, as well as SO₂ and PM_2.5 air quality monitoring. Despite the pandemic period during 2020 due to the SARS-CoV-2 virus, the aforementioned information was collected. Figure 2 shows the flow chart of the followed methodology in this research.

The main pollutant emissions produced by the maritime sector are a consequence of fuel combustion. During the development of the emission inventory, the two phases of operations carried out by a ship were considered: maneuver, that is the distance travelled by a ship between the breakwater of the port and the pier assigned to docking and hoteling, that is the stage where the ship remains at the dock for cargo loading and unloading activities and fuel supply, among others.

2.2.1. Estimated Emissions

Traffic of ships in the maneuver and hoteling phase were considered and they were classified according to the type of cargo as shown Appendix A. To know the type of engine used, information was required for each type of ship. Usually the main engine (ME) that is responsible for ship propulsion, remains turned off within the port, but it is used for loading and unloading maneuvers; the auxiliary engine (AE) generates the electrical energy to operate the lighting, ventilation, heating, information systems, computer systems and the possible pumps or cranes incorporated in the ship. The procedure used by Guevara [18], was applied (see Appendix B).

2.2.2. Air Quality and Meteorology Monitoring

An Air Quality Monitoring Station (AQMS) was deployed within the APIVER facilities at the southwest of the expansion area and 2.5 km away from the current port area at the northwest (Figure 3). Hourly concentrations of SO₂ and particles with a diameter less than 2.5 µm (PM_2.5) were measured during 15 consecutive months covering October 2019 to December 2020. Sulfur dioxide measurements were conducted using a continuous ultraviolet (UV) fluorescence analyzer model T100 (Teledyne-API). The SO₂ analyzer response was verified weekly with reference gas and zero air, calibrations were conducted bimonthly. The PM_2.5 was determined by mean of a BAM-1020 (Met-One) monitor, which was verified quarterly using calibrated flowmeter.

Meteorological measurements were done using a wireless transmitter Davis Vantage Pro2 (Davis Instruments), 10-min averages were collected with the Weather Link software. Wind sensors were located 10 m above the roof level. The 10-min averages were processed for calculating hourly averages for periods with ≥75% of valid data. Pollutants data were validated using the results of the periodical verifications calibrations, extreme values were verified against ancillary data.

3. Results and Discussion

3.1. Estimated Emissions from Ships

The estimated pollutants were (kg/month): NOx, CO, NMHC, SO₂, TPS, PM₁₀, PM_2.5, CO₂ and CH₄, results are shown in

Table 1. Total annual estimated median emissions (minimum and maximum) in 2019 and 2020.

(Kg/Year)	2019	2020	p
NOX	568 (304–937)	524 (264–908)	0.0016
CO	44 (23–71)	39 (20–67)	0.0006
NMHC	15 (8–25)	14 (7–25)	0.0018
SO2	70 (21–261)	58 (19–199)	0.0002
TSP	18 (9–29)	15.5 (8–27)	0.0003
PM10	15(7–24)	12.7 (6–22)	0.0003
PM2.5	14 (7–22)	12 (6–21)	0.0003
CO2	31,177	29,003	0.0014
	(16,786–51,628)	(14,606–50,176)
CH4	0.29 (0.16–0.49)	0.27 (0.13–0.47)	0.0014

for the years 2019 and 2020. The 2019 pollutant emissions exhibited higher values than those of 2020. The CO₂ emission from port activities were 31,177 kg/year and 29,003 kg/year for 2019 and 2020, respectively. Methane was the pollutant with the lowest estimated emission with 0.294 kg/year and 0.273 kg/year for 2019 and 2020, respectively (Appendix C,

Table A2. Total estimated emissions in 2019 by ship type in medium (maximum and minimum).

Kg/Year	RO-RO	GENERAL CARGO	TANKS	FLUIDS	BULK CARRIERS (AGR)	BULK CARRIERS (MIN)	CONTAINER CARRIER	Annual 2019
NOX	542.5	527.6	1160	205	1072	562	507.8	567.7
	(250–829)	(326–963)	(532–2072)	(147–360)	(792–1431.5)	(381–769)	(270–709)	(304–937)
CO	45.8	35	77.8	13.7	71.9	37.7	42.6	43.5
	(21–70)	(22–64.6)	(35.7–139)	(10–24)	(53–96)	(25.5–51.6)	(22.7–59.5)	(22.8–71)
NMHC	14.6	14.5	32	5.7	29.6	15.5	13	15
	(6.7–22)	(9–26.6)	(14.7–57)	(4–9.9)	(21.9–39.6)	(10.5–21)	(7–18.6)	(8–25)
SO2	278	17.6	38.8	6.9	35.8	18.8	260	70
	(128–424.8)	(11–32)	(17.8–69)	(5–12)	(26.5–48)	(12.7–25.7)	(138–363)	(21–261)
TSP	20.8	12.5	27	4.8	25	13	19.5	18
	(9.6–32)	(7.7–22.8)	(12.6–49)	(3.5–8.5)	(18.8–34)	(9–18)	(10–27)	(9–28.7)
PM10	17	10	22.5	4	20.7	11	16	14.8
	(8–26)	(6–18.7)	(10–40)	(3–7)	(15–27.7)	(7–15)	(8.5–22)	(7–23.5)
PM2.5	15.7	9	20.7	3.6	19	10	15	13.8
	(7–24)	(5.8–17)	(9.5–37)	(2.6–6)	(14–25.5)	(6.8–13.7)	(8–21)	(7–22)
CO2	30,150	28,761	63,247	11,199	58,432	30,635	28,220	31,177
	(13,917–46,053)	(17,787–52,521)	(28,994–11,298)	(8026–1965)	(43,194–78,042)	(20,769–41,927)	(15,003–39,396)	(16,786–51,628)
CH4	0.3	0.27	0.6	0.106	0.55	0.3	0.26	0.29
	(0.13–0.4)	(0.168–0.5)	(0.27–1.06)	(0.01–0.19)	(0.4–0.7)	(0.19–0.4)	(0.14–0.37)	(0.16–0.49)

and

Table A3. Total estimated emissions in 2020 by ship type in medium (maximum and minimum).

Kg/Year	RO-RO	GENERAL CARGO	TANKS	FLUIDS	BULK CARRIERS (AGR)	BULK CARRIERS (MIN)	CONTAINER CARRIER	Annual 2020
NOX	506	523	1075	203	1138	562	402	524
	(293–701)	(297–910.5)	(437–2348)	(152–483)	(760–1530.6)	(354–809)	(222.7–652.7)	(263.6–907.8)
CO	42.7	35	72	13.6	76	37.7	33.7	39
	(24.8–59)	(20–61)	(29–157)	(10–32)	(51–102.6)	(23.8–54)	(18.7–54.8)	(20–67)
NMHC	13.6	14.5	29.7	5.6	31	15.5	10.55	14
	(8–19)	(8–25)	(12–64.8)	(4–13)	(21–42)	(9.8–22)	(5.8–17)	(7–24.6)
SO2	259.5	17.5	36	6.8	38.06	18.8	206	58
	(150–359)	(10–30.5)	(14.6–78.5)	(5–16)	(25–51)	(12–27)	(114–334)	(19–199)
TSP	19	12	25	4.8	26.9	13	15	15.5
	(11–27)	(7–21.6)	(10–55.6)	(3.6–11)	(18–36)	(8–19)	(8.6–25)	(8–27)
PM10	16	10	20.83	3.9	22	11	12.6	12.7
	(9–22)	(5.8–17.7)	(8.5–45.5)	(3–9)	(14.7–29.7)	(7–15.7)	(7–20.5)	(6–22)
PM2.5	14.7	9	19	3.6	20	10	11.9	11.8
	(8.5–20)	(5–16)	(8–42)	(2.7–8.6)	(13.6–27)	(6–14)	(6.6–19)	(6–20.7)
CO2	28,137	28,530	58,608.5	11,088	62,052	30,651.5	22,359	29,003
	(16,289–38,972)	(16,200–49,641)	(23,841–127,992)	(8272–2634)	(41,447–83,448)	(19,321–44,112)	(12,375–36,277)	(14,606–50,176)
CH4	0.26	0.27	0.55	0.105	0.586	0.289	0.2	0.27
	(0.15–0.37)	(0.15–0.47)	(0.22–1.208)	(0.078–0.25)	(0.4–0.78)	(0.18–0.42)	(0.12–0.3)	(0.14–0.47)

).

Figure 4 presents the log-graph for estimated emissions in the maneuvering and hoteling stage during 2019 and 2020, in addition to the contributions by type of ships. The highest values were obtained for bulk carriers in the maneuvering stage, followed by container ships in 2019; while in 2020 there was an increase in estimated emissions in both stages specifically for bulk carriers followed by tanker ships. The increase recorded in estimated emissions was related to port activity since the number of ships in APIVER during 2020 increased to resume commercial activities that had been suspended due to the pandemic.

Regarding the hoteling activity during the study period, container ships had the highest values in the estimated emissions followed by tankers. Estimates for PM₁₀ and PM_2.5 should also be highlighted for their effects on air quality and human health [43,44,45] since it has been observed that on some occasions, they present high estimated emissions attributed to the activities of loading and unloading, mainly in bulk carriers or during the so called “Nortes” time since wind speeds increase and resuspension of soil particles can occur.

Considering the total emissions obtained in 2019 during the hoteling stage, CO₂ displayed the highest values of the estimates, followed by NO_x and SO₂. While the minimum values corresponded to CH₄ for container ships, tankers, and general cargo. On the other hand, in the maneuvering stage the highest emissions maintained the trend for CO₂, NO_X and SO₂ coming from bulk carriers followed by container ships and tankers. In 2020 during the hoteling stage, container ships depicted the highest results, followed by tankers and general cargo vessels; the order of pollutants remains as in 2019 (CO₂, NO_X and SO₂) for bulk carriers, tankers and general cargo vessels. The calculation of ship emission estimates is related to the phase in which the fuel is consumed: hoteling or maneuver, among other specific aspects.

Graphs of total emissions from docked ships show that November and December 2019 had the highest emissions of all pollutants and the same trend is presented for 2020 (Figure 5). Estimates by type of ships with oil-derived cargoes (tankers) showed the highest pollutant emissions in 2019, specifically for the months of January, June and October, for 2020 in the months of April, October and December.

As for container ships, bulk carriers had the highest pollutant emissions during the months of July, August and October 2020. For RO-RO ships, the highest emissions of NOx, CO, NMHC, CO₂, PM₁₀, PM_2.5 and CH₄ were estimated in June, while those of SO₂ were estimated in January and November (Appendix C, Table A2 and Table A3).

Emission comparisons between 2019 and 2020 showed statistically significant differences (p < 0.05) for all pollutants (Table 1). Comparing the results of the estimates by yearly seasons,

Table 2. Seasonal variation of port emissions, medians (minimum and maximum) in 2019. * Values that have a significant difference.

(kg/Year)	Spring	Summer	Autumn	Winter	p
NOx	576 (328–878)	537 (273–902)	637 (287–1161)	557 (326–864)	0.056
CO	44 (26–67)	41(20–65) *	48 (21–85.8) *	43 (24–66)	0.039
NMHC	15 (9–24)	15 (7–24)	17 (8–31)	15 (9–24)	0.062
SO2	74 (22–264)	63 (20–244)	75 (23–296)	69 (21–258)	0.258
TSP	18 (10–28)	17 (8–27) *	19 (9–34) *	18 (10–27)	0.031
PM10	15 (9–23)	14 (7–22) *	16 (7–28) *	15 (8–22)	0.031
PM2.5	14 (8–21)	13(6–21) *	15 (7–26) *	14 (7–20.8)	0.029
CO2	31,777	29,832	35,335	30,783
	(18,221–48,358)	(14,883–49,290)	(15,758–63,490)	(17,779–47,188)	0.054
CH4	0.29 (0.17–0.46)	0.28 (0.14–0.47)	0.33 (0.15–0.6)	0.290 (0.167–0.445)	0.054

presents the results as a function of medians and are compared with the Mann–Whitney U test; the pairs of variables in which significant differences were found (p < 0.05) are marked (*). During 2019, NOx and CO₂ showed higher estimated emissions than the other pollutants in all seasons, especially in the autumn. Comparing by seasons, statistically significant differences were found for CO (p = 0.039) TPS (p = 0.031 kg/year), PM₁₀ (p = 0.031 kg/year) and PM_2.5 (p = 2.5 kg/year), between summer and autumn in 2019 (

Table 3. Seasonal variation of port emissions, medians (minimum and maximum) in 2020. * Values that have a significant difference.

(kg/Year)	Spring	Summer	Autumn	Winter	p
NOx	507 (244–832) *	485.9 (255.8–858.5)	571 (306–1027) *	524 (255–921)	0.016
CO	37 (19–61) *	36.6 (20–62.8)	42 (23–74.6) *	39 (20–67)	0.016
NMHC	13.5 (6.6–22.6) *	13 (6.7–23)	15.7 (8–27) *	14 (7–25)	0.016
SO2	45 (18–158.5) *	63 (21.5–194.8)	57 (19–193)	63 (19–228) *	0.028
TSP	14 (7–25) *	15 (8–26)	16 (8.9–29.6) *	15.7 (8–28)	0.016
PM10	12 (5.8–20) *	12.5 (6.6–21)	13 (7–24) *	13 (6–23)	0.016
PM2.5	11 (5–19) *	11.7 (6–20)	12 (6.8–22.5) *	12 (6–22)	0.016
CO2	28,196	26,776	31,470	29,031	0.016
	(13,423–45,722) *	(14,035–47,025)	(16,867–56,303) *	(14,131–50,517)
CH4	0.26 (0.126–0.4) *	0.25 (0.13–0.4)	0.297 (0.16–0.5) *	0.27 (0.13–0.47)	0.016

).

In 2020, NOx and CO₂ presented also higher emissions than the other pollutants in all seasons, and the highest were during the autumn. Statistically significant differences were found for all pollutants, between the spring and autumn, however, SO₂ (p = 0.028) was found between spring and winter (Table 3) the data are presented as a function of medians accompanied by quartiles 1 and 3 (Q1–Q3).

3.2. Meteorology

Northern wind flows dominated during winter, while eastern during summer (Figure 6) As observed in the wind rose, the distribution of velocity predominates by northwestern winds with an occurrence of 10% at a speed ranging between 4 to 39.4 m s⁻¹ and North (~20% occurrence) with a speed that predominates from 6 to 34.9 m s⁻¹. Among the winds registered from the northwest to the southeast, the speeds oscillated between 4–6 and 6–34.9 m s⁻¹ (orange and cherry) in 2020. For 2019, winds with higher speeds predominated in the east direction (20% frequency of occurrence), north (<10% frequency of occurrence) with a speed of between 4–6 and 6–34.9 m s⁻¹.

Appendix D, (Figure A1 Wind roses for August–December 2019) shows that for 2019 from October to December, the northwest winds showed a higher speed of up to 40 m s⁻¹ with an occurrence of 10 to 30%. In 2020 (Appendix D, Figure A2) between January–June and September–October, the northwest winds of 6 to 34.9 m s⁻¹ predominated with an occurrence of 10–20%, whereas from July to September the winds decrease with a velocity of 4 to 6 m s⁻¹ with a maximum occurrence of 10%.

3.3. Air Quality

The pollutant concentrations are presented in time series based on 24-h daily averages (Figure 7). PM_2.5 concentrations in the study period were highest in January, April, June and December, exceeding several times the Mexican Standard for Ambient Air Quality (MAAQS 45 µg m⁻³) considering 24-h averages. For SO₂, the highest concentrations occurred in November and December in 2019 and 2020, although the averages obtained in 24 h were much smaller than the environmental regulation (MAAQS 40 ppb).

The recorded meteorological conditions are characterized by a marked period of transition between seasons. During winter the “Nortes” recurrently occur, being a coastal zone these events that last between 2 and 6 days are presented; it is characteristic that they occur in the autumn and winter months (October to March); which are related to cold air masses that decrease the temperature as well as intense winds [46] and the dispersion of pollutants in Veracruz; on the contrary, in spring the frequency of wind speeds (less than 1 m s⁻¹) inhibit the dispersion of pollutants and during the rainy season in summer, the dominant wind direction is from the east.

The reports generated at the weather station are characteristic of a coastal region, since most often the wind direction during the evening blow with components from east and south, while, during the early morning and at night, the winds bear east and north components in the months of January to April 2020.

Table 4. Basic statistics for SO₂ and PM_2.5 in Veracruz.

	SO2 (ppb)	PM2.5 (µg m−3)
Maximum Concentration	4	60.3
Average Concentration	0.6	16.4
Standard Deviation	0.4	10.9
Median	0.4	13.2

presents the results of the basic statistics of hourly pollutants averages. The high concentration values can be attributed to the transport of pollutants from areas where fossil fuel combustion processes are carried out, since the monitoring station was installed wind-tight to the southeast of the area of port expansion and northeast of the current port.

Considering the results of the wind roses for the study period, in general, ventilation was better during the winter months (December–February) than in the spring months when the dispersion of pollutant emissions could be considered poor.

The SO₂ concentrations decreased from May to October, since the rainy season occurs in Veracruz during these months, which benefits air quality. Winter begins in November and lasts until February, an increase in wind speeds is typical of the region, favoring the presence of climatic events called “Norte”, implying that the main component of the wind comes from that direction.

Considering the wind direction during the winter season in the study region, with north and northwest components, where the new port was built, the concentrations of SO₂ and PM_2.5 increased, coincident with the main sources being located in this area; for instance, since July 2019, the concessionaire ICAVE, dedicated to the transport and storage of containers, began its activities, thereby increasing the number of ships docked in the so-called “North Bay”.

PM_2.5 measurements exceeded the annual MAAQS (12 µg m⁻³) and 24-h periods (45 µg m⁻³) in March, June and December; the first two months correspond to period where “calm” prevails, causing little dispersion of pollutants. December corresponds to winter in which wind speeds are increased by frequent weather events stated above, that cause resuspension of materials. This confirms the direct correlation among port activity, air quality and seasonal weather occurring in the port of Veracruz. The simultaneous increase of SO₂ and PM_2.5 is attributed to combustion processes that can be taking place, some of which came from ships in the hoteling stage. To improve the air quality management, it may well be considered the increase of monitoring sites, including the urban area, and modelling the air quality, since the air quality monitoring station is located inside the port area (Figure 3) where the operation and expansion of the port area is carried out.

From the pollution roses prepared from the meteorological information, a seasonal variability can be established during the year, which could directly modify the behavior of the pollutants, their dispersion and the possible areas of impact. According to the graph (Figure 8A), an important contribution to PM_2.5 concentrations can be observed from the north in winter, where the construction area of the new port is located. During 2019, PM_2.5 concentrations values in autumn were between 5 and 25 µg m⁻³ with a frequency of ~30% in a western direction, while for winter, the concentration between 25 and 72 µg m⁻³ occurred in the northern and southwest directions with a frequency of ~30% and 15%, respectively.

In autumn, SO₂ concentrations ranged from 1 to 3 ppb in the eastern direction with a frequency greater than 10% and in the western direction with a frequency of approximately 30%. In winter the concentration of pollutants is present in the north (30%), east-south (~10%) and southwest with a frequency of 10% and with intervals between 1 and 5 ppb with a maximum concentration of between 6 and 18.5 ppb (Figure 8B). According to this Figure 8A, the highest PM_2.5 emissions come from the expansion area of the port of Veracruz and part of the urban area during the autumn and winter of 2019.

Figure 9 represents the seasonal pollution roses in 2020 (A) for PM_2.5 and (B) for SO₂. PM_2.5 concentrations in the range of 25 to 90 µg m⁻³ present frequencies of approximately 30% to the northeast and north in spring, while in winter, a concentration between 5 and 26 µg m⁻³ is observed from the north and southwest with frequencies of almost 30%. For SO₂ Figure 9B, in winter the highest concentration is presented with maximum values of 6 to 16.8 ppb, with a frequency greater than 20% and with a northwest and south direction. During the rest of the year, concentrations did not exceed 2 ppb. Low concentrations of SO₂ coincide with those of PM_2.5 in summer (June-September 2022) and part of autumn.

Considering the direction obtained in the rose of PM_2.5 (Figure 9A) indicates that the main source of emission in spring and winter comes from the current port of Veracruz, although there is a component from the expansion of the port in the north, possible due to the construction activities. While the highest concentrations for SO₂ (Figure 9B) are observed in winter; in both cases the main sources of emission are located in the current port area and ship areas. With this information, it can be partially concluded that the current port area is a main source contributing to pollutant emissions (SO₂ and PM_2.5) throughout the year, this behavior suggests the contribution of combustion sources from the current port and the urbanized area.

Appendix E (Figure A3 and Figure A4), presents the monthly pollutant roses for 2019 and 2020. In 2019 the PM_2.5 average was 15.2 µg m⁻³ having the highest percentage of occurrence (20%) with a maximum concentration of 72 µg m⁻³ for the winds from the west in October and November; for SO₂ the direction from west to north had a maximum occurrence of 20% with a predominant concentration of 0 to 1 ppb and 1 to 2 ppb; when winds were from east to south the concentration was higher, from 6 to 18.5 ppb with a maximum occurrence of ~15%. During 2020, winds heading northeast and southeast presented an occurrence of 10 to 20% and the highest concentrations of PM_2.5 ranged from 25 to 50 µg m⁻³; winds that go from the southwest and southwest occur with a maximum occurrence of 10% with a predominant maximum concentration of 33 to 50 µg m⁻³. For SO₂, concentrations of 0 to 1 ppb predominate with a maximum occurrence of ~15% with winds from the south, west and east; for the winds that blow to the southeast, the concentrations occurring ranged higher, with an occurrence <15%.

Appendix E, Figure A4A, shows that in the months of January–December, PM_2.5 concentrations ranged from 35 to 90 µg m⁻³ with a maximum occurrence of 30%; in the months of April, June and December 2020. The maximum concentration values were in April (25 to 90 µg m⁻³), with a maximum occurrence of 20%.

3.4. Discussion

The pollutant emissions estimated in this study coincide with those of other ports since an increase in port activities would also present an increase in pollutant estimated values [15,18,47,48]. This behavior was similar in this research, since in 2019, 1881 ships were attended and in 2020, 1374 ships. Considering the types of vessels used in this research, the estimated emissions for container ships, mineral bulk and agricultural bulk presented the highest values during April, July and October 2020, period in which activities resumed during the pandemic. In several studies, they determined that the increase in estimates of NO_X, CO₂ and SO₂ correlated with periods of increased port activity.

Regarding the temporal variability in the study area in 2019, CO₂ was the pollutant that presented the highest estimates in the four seasons of the year (spring, summer, autumn and winter) with mean values of 31 777, 29,832, 35,335 and 30,783 while the mean values of CH₄ were lower in the four seasons of the year 0.29, 0.28, 0.33, 0.290. Comparing with 2020, although there was a decrease in the values of the estimations, the tendency is maintained for CO₂ with the highest mean values in the seasons (28,196, 26,776, 31,470, 29,031) and for CH₄ with mean values of 0.26, 0.25, 0.297, 0.27 in each season. Our results can be compared with those studies presented in

Table 5. Comparison between the estimated emissions in the Port of Veracruz and the emissions in other ports.

Port	Reference	Year of Study	Pollutant T Y−1
Korea	Song and Shon (2014)	2006, 2008 and 2009	NOX = 11,700
			CO2 = 560,000
			PM = 1200
			SO2 = 9600
			COV = 374
Western Gulf of Finland	Wahlström, et al. (2006)	2006	NOX = 40,326
			PM = 1049
			SO2 = 13,456
Candarli Gulf, Turkey	Deniz, et al., 2010	2007	NOX = 632
			CO2 = 33,849
			PM = 57
			SO2 = 574
Port of Oakland, USA	Environ International Corporation (EIC) 2013	2012	NOX = 2591
			CO2 = 133,005
			PM = 67
			SO2 = 289
The Port of Oslo, Norway	Lopez-Aparicio, et al. (2017)	2013	NOX = 759
			CO2 = 56,289
			PM = 18
			SO2 = 260
Port of las Palmas, Spain	Tichavska and Tovar (2015)	2011	NOX = 4237
			CO2 = 208,697
			PM = 338
			SO2 = 1420
Qingdao	Sun, et al. (2018)	2016	NOX = 30,031.5
			CO2 = 2,347,879
			PM = 1747.14
			SO2 = 21,711.32
Port of Piraeus, Greece	Progiou, et al. (2021)	2018	NOX = 218.73
			PM10 = 15.09
			SO2 = 81.99
Veracruz, Mexico	THIS STUDY	2019 2020	NOX = 3789 CO2 = 199,900 PM = 614 SO2 = 2869 NOX = 3514 CO2 = 185,383 PM = 570 SO2 = 2662.4

. We found that the highest estimates correspond to NO_X, CO₂ and SO₂. The results of the estimates made in this study and for the afore mentioned pollutants, compared with the studies presented in Table 5, are the second highest values after those obtained in Korea in 2014 [49]. It is important to consider that the values of the other studies mentioned [50,51,52,53] even in the most recent study [54]; they are less than those shown in this research; attributed directly to the port activity and the time in which such investigations were carried out.

According to the results obtained in Figure 4, it can be observed that bulk carriers and tankers for petroleum derivatives have the highest emission of pollutants estimated in the maneuvering stage during the study period; while in hoteling the container ships exhibited the highest emission values of all pollutants [23,33,53,55,56]; this is attributed to the time spent at each stage and the number of vessels registered at APIVER. During the period evaluated in this research there is an increasing trend in the number of ships, even in the second half of 2020 during the pandemic. The values of the estimates for CO₂, NO_X and SO₂ are attributed to combustion processes, and SO₂, which is directly related to the sulfur content in the fuel used by the different types of ships.

Considering the reports of the concentrations that were generated in situ, the wind roses as well as the pollutant roses displayed concentrations values that exceeded the permissible limit (averages of 24 h of PM_2.5), which are related to the periods of greater port activity and the characteristic meteorology of a port region. This was recorded in a similar way in the research carried out by other studies [2,17,57,58], showing the importance of port emissions. The coincidence of the SO₂ and PM_2.5 highest concentrations presented in Figure 7, suggests that the fossil fuel combustion is the main source of pollutants during November and December 2019 and maybe February 2020, whereas during the other months, the PM_2.5 high values are due mainly to construction activities as well as dust resuspension. Thus, it would be advisable to continue monitoring air quality since health effects have been recorded it can induce greater morbidity and mortality from respiratory [21,59,60,61,62].

One of the activities carried out in this research has been monitoring the weather conditions and air quality despite the suspension of activities due to the pandemic period, as well as the validation of the information generated in the study area. This is obviously of great importance, given its direct relationship to the dispersion of pollutants and, consequently, to the quality of the air produced in the region.

Veracruz’s own meteorology is characteristic of a coastal region; there are cycles in some parameters such as temperature, wind direction and rainfall during the year, with monthly and seasonal variability; during most of the year, to a large extent, a northwest component is present [39,40].

The concentrations of PM_2.5 and SO₂ recorded in this research are higher in November and December 2020; specifically, for PM_2.5 in January, April, July and October 2020. For SO₂, high concentrations appear in November and December 2019. The mean concentrations of PM_2.5 were 16.4 µg m⁻³ with the highest percentage of occurrence (20%) from north and west; in the case of SO₂ it was 0.6 ppb from West to North, with a maximum occurrence of 20%. Comparing our weather and air quality results; against those presented in [62,63], they agree in presenting a relationship between the dispersion of atmospheric pollutants and meteorological conditions even when the conditions of speed and wind direction are slightly stable in Veracruz the most critical situation for dispersion is presented. Another study in Europe concluded that strong and frequent winds contribute even more to the rapid dispersion of emitted pollutants [64].

In our study, wind speeds and the prevailing direction from the northwest with an occurrence of 10% to 30% and a speed between 6 and 34.9 m s⁻¹. As can be seen from the results obtained in this research and in some other ports around the world, pollutant emissions mainly affect the air quality in the area, which has an impact on the quality of life of the population. Several port cities have implemented various programs to control emissions in ports due to port traffic [65] and it is hoped that in Veracruz they can also be applied.

4. Conclusions and Recommendations

The results of this study underline the importance of implementing a methodology that is successfully applied to various ports of the country, considering that monitoring discloses the important sources of emission of pollutants that operate in the ports, known to negatively affect the air quality of the port area and adjacent cities. Interestingly, the highest emission rates of pollutants were estimated during the major port activity; that is to say, to the increase in the number of ships that dock in the port of Veracruz. Increases in estimated emission can be attributed to the transport of pollutants from areas where activities involving combustion processes using fossil fuels are carried out.

The estimated emissions for CO₂, over the other pollutants emitted are the highest by several orders of magnitude; the total in (T Y⁻¹) 2019 and 2020 were 199,900 and 185,383 respectively.

Analyzing the pollutants emitted with the meteorological information, a seasonal variability can be established during the year, which could directly modify the behavior of the pollutants, their dispersion and the possible zones of affectation. This information shows that the current port area is a major source contributing to pollutant emissions (SO₂ and PM_2.5) throughout the year, which was observed in the pollutant roses when dominant winds came from the East—Southeast, suggesting combustion sources, although in 2020 PM_2.5 had also a contribution maybe from the construction activities.

SO₂ levels never exceeded MAAQS of 40 ppb for 24 h. In autumn, SO₂ concentrations ranged from 1 to 3 ppb in the eastern direction with a frequency greater than 10% and in the western direction with a frequency of approximately 30%. In winter the ambient air concentration was influenced from the north (30%), east-south (~10%) and southwest with a frequency of 10% and with intervals between 1 and 5 ppb.

PM_2.5 measurements exceeded the annual MAAQS (12 µg m⁻³) and 24-h periods (45 µg m⁻³) in March, June and December; the first two months correspond to period where “calm” prevails, causing unfavorable dispersion of pollutants.

The findings of this research can provide useful information for policy development on the importance of pollution sources and their impact on air quality in areas nearby ports.

In the different Mexican port areas, there is no monitoring network to follow up on air quality, so it should be considered to establish one, considering inside and outside locations of port facilities; generating real-time information on the concentrations of different types of air pollutants and assessing the potential impact on air quality in the region in general.

Once port activities are resumed after the pandemic period, it is expected that estimates of pollutants will be made to include other mobile sources, which will increase as world ports have resumed their commercial activities.

It is recommended that future work in Mexican port regions include emissions inventory for sources outside the port areas, such as industries, services and mobile vehicles, among others.

It is necessary to make a comparison with other emission inventories carried out in different ports, in order to determine the level of emission generation related to port activity before and after the pandemic.