Contributions of biomass-burning, urban, and biogenic emissions to the concentrations and light-absorbing properties of particulate matter in central Amazonia during the dry season

Journal Article · Tue Jun 18 00:00:00 EDT 2019 · Atmospheric Chemistry and Physics (Online)

DOI:https://doi.org/10.5194/acp-19-7973-2019· OSTI ID:1526775

de Sá, Suzane S.; Rizzo, Luciana V. ; Palm, Brett B. ; Campuzano-Jost, Pedro ; Day, Douglas A. ; Yee, Lindsay D.; Wernis, Rebecca; Isaacman-VanWertz, Gabriel; Brito, Joel ; Carbone, Samara; Liu, Yingjun J.; Sedlacek, Arthur ; Springston, Stephen ; Goldstein, Allen H. ; Barbosa, Henrique M. J. ; Alexander, M. Lizabeth; Artaxo, Paulo ; Jimenez, Jose L. ; Martin, Scot T.

Urbanization and deforestation have important impacts on atmospheric particulate matter (PM) over Amazonia. This study presents observations and analysis of PM₁ concentration, composition, and optical properties in central Amazonia during the dry season, focusing on the anthropogenic impacts. The primary study site was located 70 km downwind of Manaus, a city of over 2 million people in Brazil, as part of the GoAmazon 2014/5 experiment. A high-resolution time-of-flight aerosol mass spectrometer (AMS) provided data on PM₁ composition, and aethalometer measurements were used to derive the absorption coefficient b_abs,BrC of brown carbon (BrC) at 370 nm. Non-refractory PM₁ mass concentrations averaged 12.2 µ g m^-3 at the primary study site, dominated by organics (83%), followed by sulfate (11 %). A decrease inb_abs,BrC was observed as the mass concentration of nitrogen-containing organic compounds decreased and the organic PM₁ O:C ratio increased,suggesting atmospheric bleaching of the BrC components. The organic PM₁ was separated into six different classes by positive-matrix factorization(PMF), and the mass absorption efficiency E_abs associated with each factor was estimated through multivariate linear regression ofb_abs,BrC on the factor loadings. The largest E_abs values were associated with urban (2.04±0.14 m² g^-1) and biomass-burning(0.82±0.04 to 1.50±0.07 m² g^-1 ) sources. Together, these sources contributed at least 80 % ofb_abs,BrC while accounting for 30 % to 40 % of the organic PM₁ mass concentration. In addition, a comparison of organic PM₁ composition between wet and dry seasons revealed that only part of the 9-fold increase in mass concentration between the seasons can be attributed to biomass burning. Biomass-burning factor loadings increased by 30-fold,elevating its relative contribution to organic PM₁ from about 10 % in the wet season to 30 % in the dry season. However, most of the PM₁ mass (>60 %) in both seasons was accounted for by biogenic secondary organic sources, which in turn showed an 8-fold seasonal increase in factor loadings. A combination of decreased wet deposition and increased emissions and oxidant concentrations, as well as a positive feedback on larger mass concentrations are thought to play a role in the observed increases. Furthermore, fuzzy c -means clustering identified three clusters, namely “baseline”, “event”, and “urban” to represent different pollution influences during the dry season. The baseline cluster,representing the dry season background, was associated with a mean mass concentration of 9±3 µ g m^-3 . This concentration increased on average by 3 µ g m^-3 for both the urban and the event clusters.The event cluster, representing an increased influence of biomass burning and long-range transport of African volcanic emissions, was characterized by remarkably high sulfate concentrations. The urban cluster, representing the influence of Manaus emissions on top of the baseline, was characterized by an organic PM₁ composition that differed from the other two clusters.The differences discussed suggest a shift in oxidation pathways as well as an accelerated oxidation cycle due to urban emissions, in agreement with findings for the wet season.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: SC0011115; AC05-76RL01830; ASR (grant no. SC0011115); SC0012704; SC0011105; SC0006680; SC0016559
• OSTI ID: 1526775
• Alternate ID(s): OSTI ID: 1542099; OSTI ID: 1559997; OSTI ID: 1566765
• Report Number(s): BNL-212043-2019-JAAM; PNNL-SA-147396
• Journal Information: Atmospheric Chemistry and Physics (Online), Journal Name: Atmospheric Chemistry and Physics (Online) Vol. 19 Journal Issue: 12; ISSN 1680-7324
• Publisher: Copernicus Publications, EGU
• Country of Publication: Germany
• Language: English

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54 ENVIRONMENTAL SCIENCES