Study of formaldehyde (HCHO) columns abundance from OMI satellite data in two agricultural regions in the south of Mexico

HCHO is one of the most abundant carbonyl compounds in the troposphere. At global scale, HCHO is mainly produced from the oxidation of volatile organic compounds (VOC) which come from biogenic (predominantly isoprene) emissions, biomass burning, and anthropogenic emissions. HCHO is produced in high amounts when both isoprene and nitrogen oxides (NO_x, NO + NO₂) are present. In order to determine the driver factors and the principal months of enhancement of HCHO over the Oaxaca and the Chiapas regions, important rain-fed maize agricultural areas located in the south of Mexico, HCHO columns from the Ozone Monitoring Instrument (OMI) were used in conjunction with isoprene emissions, NO_x  emissions from biomass burning (NO_{x_bb}), and NO_x emissions from soils with their different sources (biomes: NO_{x_bio}, fertilization and manure: NO_{x_fer,} deposition of N: NO_{x_dep}, pulses: NO_{x_pul}, and total: NO_{x_tot}) from January 2005 to December 2016. Based on scatterplots, Spearman rank correlations, and multiple regression models, we determined that isoprene and NO_{x_bb} were important drivers of HCHO abundance in the Oaxaca region, especially in April and May. In the Chiapas region, important drivers were isoprene, NO_{x_bb}, and NO_{x_fer}, mainly from April to August. With the estimated regression coefficients, the contribution (in %) of the relevant emission fluxes for each region were calculated in order to know which source was the predominant one in the exacerbation of modeled HCHO (HCHO_MOD). In the Oaxaca region, isoprene predominates over NO_{x_bb}. In the Chiapas region, the emissions of NO_x were more importantthan isoprene. NO_{x_bb} and NO_{x_fer} were enhanced principally due to the agricultural activity taking place in the Oaxaca and the Chiapas regions. Thus, this work demonstrates the impact of agricultural activity on HCHO columns observed by the OMI instrument.