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The atmospheric chemistry of isoprene contributes to the productionof a substantial mass fraction of the particulate matter (PM) over tropicalforests. Isoprene epoxydiols (IEPOX) produced in the gas phase by theoxidation of isoprene under HO2-dominant conditions are subsequentlytaken up by particles, thereby leading to production of secondary organic PM.The present study investigates possible perturbations to this pathway byurban pollution. The measurement site in central Amazonia was located 4 to6 h downwind of Manaus, Brazil. Measurements took place from Februarythrough March 2014 of the wet season, as part of theGoAmazon2014/5experiment. Mass spectra of organic PM collected with an Aerodyne AerosolMass Spectrometer were analyzed by positive-matrix factorization. Oneresolved statistical factor (<q>IEPOX-SOA factor</q>) was associated with PMproduction by the IEPOX pathway. The IEPOX-SOA factor loadings correlatedwith independently measured mass concentrations of tracers of IEPOX-derivedPM, namely C5-alkene triols and 2-methyltetrols (R = 0. 96 and 0.78,respectively). The factor loading, as well as the ratio f of the loading toorganic PM mass concentration, decreased under polluted compared tobackground conditions. For an increase in NOy concentration from 0.5 to2 ppb, the factor loading and f decreased by two to three fold. Overall,sulfate concentration explained 37 % of the variability in the factorloading. After segregation of factor loading into subsets based on NOyconcentration, the sulfate concentration explained up to 75 % of thevariability. Considering both factors, the data sets show that thesuppressing effects of increased NO concentrations dominated over theenhancing effects of higher sulfate concentrations. The pollution from Manauselevated NOy concentrations more significantly than sulfateconcentrations relative to background conditions. In this light, increasedemissions of nitrogen oxides, as anticipated for some scenarios of Amazonianeconomic development, could significantly alter pathways of PM productionthat presently prevail over the tropical forest, implying changes to airquality and regional climate

Influence of urban pollution on the production of organic particulate matter from isoprene epoxydiols in central Amazonia