Content and composition of dissolved organic carbon in precipitation at the southern part of Mexico City

Abstract

We present concentrations of dissolved total carbon (TC) and organic carbon (OC) in rainwater samples collected in 2016 in the southern part of Mexico City in a preliminary study. TC ranged from 10 to 25 mgC L^–1 and OC – reported as non-purgable organic carbon (NPOC) – varied between 2.5 and 20 mgC L^–1. NPOC concentrations were higher in samples collected between May and July and a change in the ratio of NPOC/TC was detected for the second part of the campaign (i.e., August-October). ¹H NMR analysis indicated presence of aldehydes, carboxylic and other oxygenated hydrocarbons in the precipitation. An evaluation of air mass back-trajectories suggested no relationship between the organic contents and wind directions. Carbon contents were originated from sources within the basin of Mexico and higher pH of rainwater during the passage of air masses indicates that the sources causing rain neutralization are located in northern parts of the city.