Molecular composition of organic aerosols in central Amazonia: an
ultra-high-resolution mass spectrometry study
Ivan Kourtchev1,2,Ricardo H. M. Godoi3,Sarah Connors1,James G. Levine4,Alex T. Archibald1,5,Ana F. L. Godoi3,Sarah L. Paralovo3,Cybelli G. G. Barbosa3,Rodrigo A. F. Souza6,Antonio O. Manzi7,Roger Seco8,Steve Sjostedt9,Jeong-Hoo Park10,Alex Guenther8,11,Saewung Kim8,James Smith12,13,Scot T. Martin14,15,and Markus Kalberer1Ivan Kourtchev et al. Ivan Kourtchev1,2,Ricardo H. M. Godoi3,Sarah Connors1,James G. Levine4,Alex T. Archibald1,5,Ana F. L. Godoi3,Sarah L. Paralovo3,Cybelli G. G. Barbosa3,Rodrigo A. F. Souza6,Antonio O. Manzi7,Roger Seco8,Steve Sjostedt9,Jeong-Hoo Park10,Alex Guenther8,11,Saewung Kim8,James Smith12,13,Scot T. Martin14,15,and Markus Kalberer1
1Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW,
UK
2Department of Chemistry and Environmental Research Institute,
University College Cork, Cork, Ireland
3Environmental Engineering Department, Federal University of Parana,
Curitiba, Brazil
4School of Geography Earth & Environmental Sciences, University of
Birmingham, Birmingham, B15 2TT, UK
5NCAS climate, University of Cambridge, Cambridge, CB2 1EW, UK
6State University of Amazonas, Av. Darcy Vergas, 1200, 69065-020,
Manaus-AM, Brazil
7Instituto Nacional de Pesquisas da Amazônia (INPA), Clima e
Ambiente (CLIAMB), Manaus-AM, Brazil
8Department of Earth System Science, University of California,
Irvine,
CA 92697, USA
9NOAA ESRL Chemical Sciences Division, Boulder, CO, USA
10Air Quality Forecasting Center, National Institute of Environmental Research, Republic of Korea
11Pacific Northwest National Laboratory, Richland, WA, USA
12Atmospheric Chemistry Division, National Center for Atmospheric
Research, Boulder, CO, USA
13Department of Chemistry, University of California, Irvine, CA, USA
14School of Engineering and Applied Science, Harvard University, Cambridge, MA 02138, USA
15Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
Received: 14 May 2016 – Discussion started: 25 May 2016 – Revised: 12 Aug 2016 – Accepted: 31 Aug 2016 – Published: 23 Sep 2016
Abstract. The Amazon Basin plays key role in atmospheric chemistry, biodiversity and climate change. In this study we applied nanoelectrospray (nanoESI) ultra-high-resolution mass spectrometry (UHRMS) for the analysis of the organic fraction of PM2.5 aerosol samples collected during dry and wet seasons at a site in central Amazonia receiving background air masses, biomass burning and urban pollution. Comprehensive mass spectral data evaluation methods (e.g. Kendrick mass defect, Van Krevelen diagrams, carbon oxidation state and aromaticity equivalent) were used to identify compound classes and mass distributions of the detected species. Nitrogen- and/or sulfur-containing organic species contributed up to 60% of the total identified number of formulae. A large number of molecular formulae in organic aerosol (OA) were attributed to later-generation nitrogen- and sulfur-containing oxidation products, suggesting that OA composition is affected by biomass burning and other, potentially anthropogenic, sources. Isoprene-derived organosulfate (IEPOX-OS) was found to be the most dominant ion in most of the analysed samples and strongly followed the concentration trends of the gas-phase anthropogenic tracers confirming its mixed anthropogenic–biogenic origin. The presence of oxidised aromatic and nitro-aromatic compounds in the samples suggested a strong influence from biomass burning especially during the dry period. Aerosol samples from the dry period and under enhanced biomass burning conditions contained a large number of molecules with high carbon oxidation state and an increased number of aromatic compounds compared to that from the wet period. The results of this work demonstrate that the studied site is influenced not only by biogenic emissions from the forest but also by biomass burning and potentially other anthropogenic emissions from the neighbouring urban environments.
