Chemical Signatures of Seasonally Unique Anthropogenic Influences on Organic Aerosol Composition in the Central Amazon

Urbanization and fires perturb the quantities and composition of fine organic aerosol in the central Amazon, with ramifications for radiative forcing and public health. These disturbances include not only direct emissions of particulates and secondary organic aerosol (SOA) precursors but also changes in the pathways through which biogenic precursors form SOA. The composition of ambient organic aerosol is complex and incompletely characterized, encompassing millions of potential structures relatively few of which have been synthesized and characterized. Through analysis of submicron aerosol samples from the Green Ocean Amazon (GoAmazon2014/5) field campaign by twodimensional gas chromatography coupled with machine learning, similar to 1300 unique compounds were traced and characterized over two seasons. Fires and urban emissions produced chemically and interseasonally distinct impacts on product signatures, with only similar to 50% of compounds observed in both seasons. Seasonally unique populations point to the importance of aqueous processing in Amazonian aerosol aging, but further mechanistic insights are impeded by limited product identity knowledge. Less than 10% of compounds were identifiable at an isomer-specific level. Overall, the findings (i) provide compositional characterization of anthropogenic influence on submicron organic aerosol in the Amazon, (ii) identify key season-to-season differences in chemical signatures, and (iii) highlight high-priority knowledge gaps in current speciated knowledge.

Automated summary

Urbanization and fires have a significant impact on the quantities and composition of organic aerosol in the central Amazon, affecting radiative forcing and public health. The composition of ambient organic aerosol is complex and not fully understood, with limited knowledge about the different compounds present. Through analysis of aerosol samples, it was found that fires and urban emissions have distinct effects on the chemical signatures, and only a portion of compounds were observed in both seasons. This study highlights the need for further research to fill the knowledge gaps in understanding the speciation of organic aerosol in the Amazon.