Particulate Carbon, a Significant Contributor to The Visibility Reduction of Mexico City

Abstract

Total particulate elemental carbon concentrations (Ct) incluoing organic volatile (C0 v) and black carbon {Cb), were determined in 92 stored high-volume sampled filters collected during 1982 in a 24 hr sampling period with an alternative schedule. Coarse and fine particulate mass (CFPM) were sampled at the same schedule and site using a modified Anderson sampler. The sampling site "El Casco de Santo Tomas", is located near the Mexico City's downtown area. The results show that Ct ranged from 14.8 to 98.7 p.g/m3 . The total suspended particulate (TSP) mean concentration was 204 p.g/m3. The Ct. C0v and Cb mean concentrations content in the TSP were 49.87, 32.3 and 16.9 p.g/m3 respectively. The statistical analysis of Ct and Cb on TSP data shows a correlation coefficient of 0.81 and 0.9 respectively; C0v results from: C0v = Ct - Cb· The CFPM mean concentration was 154 p.g/m3 (0.5 p.m mass median diameter), but Ct was not determined. Using both specific light-absorption and light-scattering coefficients estimating procedures reported by several authors, and sulfate and nitrate data from the Tacubaya Observatory sampling station, 5.6 km from the first one, the contribution of the elemental carbon to the estimated visibility reduction was deduced to be near 50%. The estimated visibility using the Koschmicdcr relationship and the extinction coefficient (bext= 7.64 x 1<r"m-1) obtained from the data was 5.10 km. The average visibility reported by the Tacubaya Observatory Station was 6.3 km for the same period.