Carbonaceous particles and PM2.5 optical properties in Mexico City during the ACU15 campaign

We measured the optical properties of aerosols with two photoacoustic spectrometers operating at 532 and 870 nm wavelengths and sampled PM2.5 to analyze the organic carbon (OC) and elemental carbon (EC) content. The measuring site was in the southwest corner of Mexico City. We sorted the data by OC/EC ratios and calculated four mass absorption efficiencies (MAEs) for each wavelength with linear regressions. The MAEs ranged from 2.27 to 19.75 and 2.03 to 15.26 m(2) g(-1) at 532 and 870 nm, respectively, with determination coefficients above 0.88, showing that the amount of OC modifies the absorption properties of particles, sometimes underestimating or overestimating the black carbon concentration. It is possible to choose the MAE based on the daily median O-3 concentration when there is no information about the EC and OC composition.