Mass Absorption Efficiency of PM1 in Mexico City during ACU15

Abstract

From January to March 2015, an atmospheric aerosol measurement campaign, “Aerosoles en Ciudad Universitaria 2015” (ACU15), was carried out in Mexico City to determine the particles’ optical properties and chemical composition. Two photoacoustic spectrometers measured the scattering and absorption coefficient at two different wavelengths. The average absorption coefficient at 532 nm was 12.71 ± 9.48 Mm−1 and at 870 nm was 10.35 ± 7.36 Mm−1. The average scattering coefficient was 65.63 ± 47.12 Mm−1 (532 nm) and 21.12 ± 14.24 Mm−1 (870 nm). The chemical composition was determined via an aerosol chemical speciation monitor. The organic aerosol fraction represented 53% of the total PM1 and was made up of 63% low volatile (4.64 µg m−3), 22% hydrogenated (1.90 µg m−3), and 15% semi-volatile organics (1.54 µg m−3). The correlation coefficient of chemical species (NO3−, NH4+, SO42−, low-volatile, and semi-volatile organics) and optical properties was 0.92. The multilinear regression showed a good agreement among chemical species and optical properties (r > 0.7). The mass absorption coefficient calculated for the measuring site at 870 nm was MAE870 = 5.8 m2 g−1, instead of the default 4.74 m2 g−1. Furthermore, based on the median AAE, the 532 nm MAE532 resulting from the multiple linear regression (MLR) showed the following coefficients: 7.70 m2 g−1 (eBC), 0.22 m2 g−1 (HOA), and 0.16 m2 g−1 (LV–OOA). The coefficients of MLR were: 7.08 m2 g−1 (eBC), 5.83 m2 g−1 (NO3−), 5.69 m2 g−1 (low volatile organic aerosol), 2.78 m2 g−1 (SO42−), 2.40 m2 g−1 (hydrocarbon-like organic aerosol), and 1.04 m2 g−1 (semi volatile organic aerosol).