Organic composition and source apportionment of fine aerosol at Monterrey, Mexico, based on organic markers

Abstract

Abstract. Primary emissions from anthropogenic and biogenic sources as well as secondary formation are responsible for the pollution levels of ambient air in major urban areas. These sources release fine particles into the air that negatively impact human health and the environment. Organic molecular markers, which are compounds that are unique to specific PM2.5 sources, can be utilized to identify the major emission sources in urban areas. In this study, 43 representative PM2.5 samples, for both daytime and nighttime periods, were built from individual samples collected in an urban site of the Monterrey metropolitan area (MMA) during the spring and fall of 2011 and 2012. The samples were analyzed for organic carbon, elemental carbon, and organic molecular markers. Several diagnostic tools were employed for the preliminary identification of emission sources. Organic compounds for eight compound classes were quantified. The n-alkanoic acids were the most abundant, followed by n-alkanes, wood smoke markers, and levoglucosan/alkenoic acids. Polycyclic aromatic hydrocarbons (PAHs) and hopanes were less abundant. The carbon preference index (0.7–2.6) for n-alkanes indicates a major contribution of anthropogenic and mixed sources during the fall and the spring, respectively. Hopanes levels confirmed the contribution from gasoline and diesel engines. In addition, the contribution of gasoline and diesel vehicle exhaust was confirmed and identified by the PAH concentrations in PM2.5. Diagnostic ratios of PAHs showed emissions from burning coal, wood, biomass, and other fossil fuels. The total PAHs and elemental carbon were correlated (r2 = 0.39–0.70) across the monitoring periods, reinforcing that motor vehicles are the major contributors of PAHs. Cholesterol levels remained constant during the spring and fall, showing evidence of the contribution of meat-cooking operations, while the isolated concentrations of levoglucosan suggested occasional biomass burning events. Finally, source attribution results obtained using the CMB (chemical mass balance) model indicate that emissions from motor vehicle exhausts are the most important, accounting for the 64 % of the PM2.5, followed by meat-cooking operations with 31 % The vegetative detritus and biomass burning had the smallest contribution (2.2 % of the PM2.5). To our knowledge, this is only the second study to explore the organic composition and source apportionment of fine organic aerosol based on molecular markers in Mexico and the first for the MMA. Particularly molecular marker were quantified by solvent extraction with dichloromethane, derivatization, and gas chromatography with mass spectrometry (GC/MS).

Application of partial least squares as a complementary and preliminary receptor model for source apportionment of ambient aerosol based on molecular organic markers

“…As shown in the CMB results in Mancilla et al (Table ), PLS resolved similar source profiles to CMB, with the advantage that the source profiles and their uncertainties, as well as the uncertainties of ambient concentrations, were not required. Differences between these methods could be attributed to the nature of the source profiles used for CMB, as profiles can be similar between locations but not equal.…”

“…The vegetation around the sampling site included dispersed and scarce grass, shrubs, and street tree systems in the immediate vicinity, as well as in the periphery. The sampling site was selected based on coefficients of divergence analysis using 24‐hour average PM 2.5 concentrations recorded by the local air monitoring network …”

“…The sampling site was selected based on coefficients of divergence analysis using 24-hour average PM 2.5 concentrations recorded by the local air monitoring network. 22 The samples were collected during both the spring and fall in 2011 and 2012. Consecutive 12-hour samples were taken each sampling day to obtain information for daytime and nighttime periods.…”

“…To test this, the results obtained through the application of PLS were compared with those obtained from PMF and CMB. Organic speciation of ambient PM 2.5 reported by Mancilla et al was used to quantify the contribution from different emission sources to the ambient fine particles in the MMA. To compensate the use of an unweighted variance PLS receptor model to estimate the relative source contributions, PLS was combined with a Monte Carlo sampling (MC‐S) approach.…”

Determination of n-alkanes, polycyclic aromatic hydrocarbons and hopanes in atmospheric aerosol: evaluation and comparison of thermal desorption GC-MS and solvent extraction GC-MS approaches

“…A portion (4.34 cm 2 ) of the sample (i.e., blank) filter was cut with a clean stainless steel punch, then extracted with a mixture (15 mL) of dichloromethane (DCM) (99.9 %, LC grade, Mallinckrodt Laboratory Chemicals, Phillipsburg, NJ, USA) and methanol (99.9 %, LC grade, Mallinckrodt Laboratory Chemicals, Phillipsburg, NJ, USA) (3 : 1, v/v) under ultra-sonication for 15 min and filtered through quartz wool packed in a Pasteur pipette (Fujii et al, 2016;Mohseni Bandpi et al, 2017). The extraction procedure was repeated three times.…”