Influence of Anthropogenic Emissions on the Production of Organic Particulate Matter During GoAmazon2014/5

As part of GoAmazon2014/5, a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed to characterize the composition of fine-mode particulate matter (PM) and provide insights into the production of airborne particle material in the central Amazon basin, Brazil. The focus was on the influence of biogenic-anthropogenic interactions on the measured aerosol particles, especially as related to the formation of organic PM. Through a combination of meteorology, emissions, and chemistry, the T3 research site (located 70 km downwind of Manaus) was affected by biogenic emissions from the tropical rainforest that were periodically mixed with urban outflow from the Manaus metropolitan area as well as with biomass burning plumes. Results from the T3 site are presented in the context of measurements at T0a (ATTO) and T2, representing predominantly clean and polluted conditions, respectively. At T3, in the wet season (1/Feb - 31/Mar 2014) the non-refractory PM1 mass concentration had values on order of 1 to 2 μg/m3, while in the dry season (15/Aug - 15/Oct 2014) PM1 was eight times higher. In both seasons, the organic component was dominant, contributing 80-85% by mass.

The analysis of the results aims at delineating the anthropogenic impact on the measurements, especially focusing on anthropogenic sulfate as a mediator. Positive matrix factorization (PMF) analysis is applied to the time series of organic particle mass spectra. The factors and their loadings provide information on the relative and time-varying contributions of different sources and processes of organic PM. A factor associated with secondary organic material produced from the reactive uptake of epoxydiols (a product of isoprene photooxidation under HO2-dominant conditions) is resolved for both seasons (hereafter, IEPOX-SOA). The time trends of the factors, especially of IEPOX-SOA, are investigated against co-located measurements, toward the goal of improving the understanding of anthropogenic influences on the mass concentrations and composition of PM1.