Document Type

Article

Publication Date

6-6-2017

Publication Title

Atmospheric Chemistry and Physics

ISSN

1680-7324

Volume

17

Issue

11

DOI

https://doi.org/10.5194/acp-17-6611-2017

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 6h 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. The IEPOX-SOA factor loadings 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). The factor loading, as well as the ratio f of the loading to organic PM mass concentration, decreased under polluted compared to background conditions. For an increase in NOy concentration from 0.5 to 2ppb, the factor loading and f decreased by two to three fold. Overall, sulfate concentration explained 37% of the variability in the factor loading. After segregation of factor loading into subsets based on NOy concentration, the sulfate concentration explained up to 75% of the variability. Considering both factors, the data sets show that the suppressing effects of increased NO concentrations dominated over the enhancing effects of higher sulfate concentrations. The pollution from Manaus elevated NOy concentrations more significantly than sulfate concentrations relative to background conditions. 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.

Comments

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. Martin1,11

  • 1School 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, Brazil
  • 7Instituto Nacional de Pesquisas da Amazonia, Manaus, Amazonas, Brazil
  • 8Escola Superior de Tecnologia, Universidade do Estado do Amazonas, Manaus, Amazonas, Brazil
  • 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

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Creative Commons Attribution 3.0 License
This work is licensed under a Creative Commons Attribution 3.0 License.

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