Analysis of tropospheric ozone and carbon monoxide profiles over South America based on MOZAIC/IAGOS database and model simulations

Abstract

In this study, we analyzed ozone and carbon monoxide profiles measured, during landing and taking off over Caracas, in Venezuela, and Rio de Janeiro and São Paulo, in Brazil, by commercial aircrafts from the MOZAIC/IAGOS fleet. The analyzed database include years from 1994 to 2009 over Caracas, from 1994 to 2005 over São Paulo, from 1994 to 2004 and 2012 over Rio de Janeiro. In terms of ozone concentrations, results showed clean atmosphere over Caracas with seasonal mean partial ozone column, integrated from the surface up to 200 hPa, of less than 25 DU, presenting the highest seasonal mean in March, April and May. During this season, carbon monoxide concentration reached values as high as 400 ppbv below 750 hPa, particularly in the years 2003 and 2007. Backward trajectories analyses with FLEXPART, of case studies for which the measured concentrations were high, showed that local sources were the main contributors to the observed loadings. Fire pixels from MODIS indicated local biomass burning activities as the possible source, since the period corresponds to the peak of the dry season above the equator, once the ITCZ is further south. Sensitivity studies performed with the chemical transport model GEOS-Chem version 9-01-01 could not capture the influence of biomass burning, what could be due to an underestimation of GFED v2, the emission inventory used in this study. Over São Paulo and Rio de Janeiro, the highest ozone concentration was observed during September to November, with mean partial ozone column, integrated from the surface up to 200 hPa, reaching about 30 DU in 2012. Lightning and biomass burning from South America and local urban pollutions were the main sources of ozone precursors with no contribution of long range transport from Africa. Although no trend analysis could be performed due to the rather irregular frequency of flights over this area, results indicated a possible tendency of increasing concentrations in the recent years at 95% significance level