Influence of urban pollution on the production of organic particulate matter from isoprene epoxydiols in central Amazonia
Suzane S. de Sá1, Brett B. Palm2, Pedro Campuzano-Jost2, Douglas A. Day2, Matthew K. Newburn3, Weiwei Hu2, Gabriel Isaacman-VanWertz4,a, Lindsay D. Yee4, Ryan Thalman5, Joel Brito6,b, Samara Carbone6, Paulo Artaxo6, Allen H. Goldstein4, Antonio O. Manzi7, Rodrigo A.F. Souza8, Fan Mei9, John E. Shilling3,9, Stephen R. Springston5, Jian Wang5, Jason D. Surratt10, M. Lizabeth Alexander3, Jose L. Jimenez2, and Scot T. Martin1,111School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA 2Department of Chemistry & Biochemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA 3Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington, USA 4Dept. of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA 5Brookhaven National Laboratory, Upton, New York, USA 6Departamento de Física Aplicada, Universidade de São Paulo, São Paulo, Brasil 7Instituto Nacional de Pesquisas da Amazonia, Manaus, Amazonas, Brasil 8Escola Superior de Tecnologia, Universidade do Estado do Amazonas, Manaus, Amazonas, Brasil 9Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA 10Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA 11Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA anow at: Massachusetts Institute of Technology, Cambridge, Massachusetts, USA bnow at: Laboratory for Meteorological Physics (LaMP), University Blaise Pascal, Aubière, France
Received: 16 Nov 2016 – Accepted for review: 08 Dec 2016 – Discussion started: 13 Dec 2016
Abstract. The atmospheric chemistry of isoprene contributes to the production of a substantial mass fraction of the particulate matter (PM) over tropical forests. Isoprene epoxydiols (IEPOX) produced in the gas phase by the oxidation of isoprene under HO2-dominant conditions are subsequently taken up by particles, thereby leading to production of secondary organic PM. The present study investigates possible perturbations to this pathway by urban pollution. The measurement site in central Amazonia was located 4 to 6 hours downwind of Manaus, Brazil. Measurements took place from February through March 2014 of the wet season, as part of the GoAmazon2014/5 experiment. Mass spectra of organic PM collected with an Aerodyne Aerosol Mass Spectrometer were analyzed by positive-matrix factorization. One resolved statistical factor (“IEPOX-SOA factor”) was associated with PM production by the IEPOX pathway. Loadings of this factor correlated with independently measured mass concentrations of tracers of IEPOX-derived PM, namely C5-alkene triols and 2-methyltetrols (R = 0.96 and 0.78, respectively). Factor loading, as well as the ratio of the factor loading to organic PM mass concentration, decreased under polluted compared to background conditions. For the study period, sulfate concentration explained 37 % of the variability in the factor loading. After segregation of the data set by NOy concentration, the sulfate concentration explained up to 75 % of the variability in factor loading within the NOy subsets. The sulfate-detrended IEPOX-SOA factor loading decreased by two- to three-fold for an increase in NOy concentration from 0.5 to 2 ppb. The suppressing effects of elevated NO dominated over the enhancing effects of higher sulfate with respect to the production of IEPOX-derived PM. Relative to background conditions, the Manaus pollution contributed more significantly to NOy than to sulfate. In this light, increased emissions of nitrogen oxides, as anticipated for some scenarios of Amazonian economic development, could significantly alter pathways of PM production that presently prevail over the tropical forest, implying changes to air quality and regional climate.
de Sá, S. S., Palm, B. B., Campuzano-Jost, P., Day, D. A., Newburn, M. K., Hu, W., Isaacman-VanWertz, G., Yee, L. D., Thalman, R., Brito, J., Carbone, S., Artaxo, P., Goldstein, A. H., Manzi, A. O., Souza, R. A. F., Mei, F., Shilling, J. E., Springston, S. R., Wang, J., Surratt, J. D., Alexander, M. L., Jimenez, J. L., and Martin, S. T.: Influence of urban pollution on the production of organic particulate matter from isoprene epoxydiols in central Amazonia, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1020, in review, 2016.