Spatial differences in ambient coarse and fine particles in the Monterrey metropolitan area, Mexico: Implications for source contribution

Abstract

The ambient air of the Monterrey Metropolitan Area (MMA) in Mexico frequently exhibits high levels of PM 10 and PM 2.5. However, no information exists on the chemical composition of coarse particles (PM c = PM 10-PM 2.5). A monitoring campaign was conducted during the summer of 2015, during which 24-hr average PM 10 and PM 2.5 samples were collected using high-volume filter-based instruments to chemically characterize the fine and coarse fractions of the PM. The collected samples were analyzed for anions (Cl-, NO 3-, SO 4 2-), cations (Na + , NH 4 + , K +), organic carbon (OC), elemental carbon (EC), and 35 trace elements (Al to Pb). During the campaign, the average PM 2.5 concentrations did not showed significance differences among sampling sites, whereas the average PM c concentrations did. In addition, the PM c accounted for 75% to 90% of the PM 10 across the MMA. The average contribution of the main chemical species to the total mass indicated that geological material including Ca, Fe, Si, and Al (45%) and sulfates (11%) were the principal components of PM c , whereas sulfates (54%) and organic matter (30%) were the principal components of PM 2.5. The OC-to-EC ratio for PM c ranged from 4.4 to 13, whereas that for PM 2.5 ranged from 3.97 to 6.08. The estimated contribution of Secondary Organic Aerosol (SOA) to the total mass of organic aerosol in PM 2.5 was estimated to be around 70-80%; for PM c , the contribution was lower (20-50%). The enrichment factors (EF) for most of the trace elements exhibited high values for PM 2.5 (EF: 10-1000) and low values for PM c (EF: 1-10). Given the high contribution of crustal elements and the high values of EFs, PM c is heavily influenced by soil resuspension and PM 2.5 by anthropogenic sources. Finally, the airborne particles found in the eastern region of the MMA were chemically distinguishable from those in its western region. Implications: Concentration and chemical composition patterns of fine and coarse particles can vary significantly across the MMA. Public policy solutions have to be built based on these observations. There is clear evidence that the spatial variations in the MMA's coarse fractions are influenced by clearly recognizable primary emission sources, while fine particles exhibit a homogeneous concentration field and a clear spatial pattern of increasing secondary contributions. Important reductions in the coarse fraction can come from primary particles' emission controls; for fine particles, control of gaseous precursors-particularly sulfur-containing species and organic compounds-should be considered.

Spatial and Temporal Distribution of PM2.5 Pollution over Northeastern Mexico: Application of MERRA-2 Reanalysis Datasets

“…Thus, the wind components from MERRA-2 were not incorporated into the NN model. According to the data extracted from MERRA-2, during most of the study period, the main components of PM2.5 were sulfates (33%) and OC (29%) (Figure 6), which were similar to the findings of Martínez et al According to the data extracted from MERRA-2, during most of the study period, the main components of PM 2.5 were sulfates (33%) and OC (29%) (Figure 6 [48] revealed that anthropogenic sources were typically associated with high contributions of SO 4 2− , OM, and BC. Secondary inorganic aerosols in the form of ammonium nitrates that were not reported by MERRA-2 were found to be important compounds in the MMA [81].…”

“…In contrast to other Mexican cities that have improved their air quality, the average concentrations of PM 2.5 in the MMA increased by~5 µg m −3 between 2013 and 2015 [47]. In routine monitoring network, annual averages of PM 2.5 were found in the range of 20-34 µg m −3 , which exceeded the corresponding national air quality standards of 12 µg m −3 (annual average) [48]. Annual seasonal variations in the concentration of PM 2.5 were observed, in which the highest concentration was in winter, and the lowest concentration was in the first half of the fall season [49].…”

Evaluation of MODIS Aerosol Optical Depth and Surface Data Using an Ensemble Modeling Approach to Assess PM2.5 Temporal and Spatial Distributions

“…The data distribution of the variables in the best dataset is shown in Figure 4. In general, PM 2.5 and the meteorological variables displayed behavior typical of the region [32,53]. The ground-based temperature (Figure 4a) increased from April to August.…”

“…Large amounts of atmospheric dust might result in high AOD values [69]. Mancilla et al (2019) [32] also reported that (NH4)2SO4 can contribute to as much as 54% of the total mass of PM2.5 in the MMA. According to Gao and Zhang (2014) [70], the extinction coefficient increases with increased SO2 −4 , therefore yielding larger AOD values, as it is the integral of the aerosol extinction coefficient.…”

“…The MMA currently has a status of nonattainment with respect to the Mexican Air Quality Standards for PM 2.5 [30,31]. In 2015, the MMA exhibited annual averages in the range of 20-34 µg m −3 for PM 2.5 , exceeding the PM 2.5 national air quality standard of 12 µg m −3 [32]. For 50 days of 2019, the PM 2.5 concentrations exceeded the 24-h average limit of 45 µg m −3 set by the Mexican standard [33].…”