Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), key isoprene oxidation products, with inorganic sulfate aerosol yields substantial amounts of secondary organic aerosol (SOA) through the formation of organosulfur compounds. The extent and implications of inorganic-to-organic sulfate conversion, however, are unknown. In this article, we demonstrate that extensive consumption of inorganic sulfate occurs, which increases with the IEPOX-to-inorganic sulfate concentration ratio (IEPOX/Sulfinorg), as determined by laboratory measurements. Characterization of the total sulfur aerosol observed at Look Rock, Tennessee, from 2007 to 2016 shows that organosulfur mass fractions will likely continue to increase with ongoing declines in anthropogenic Sulfinorg, consistent with our laboratory findings. We further demonstrate that organosulfur compounds greatly modify critical aerosol properties, such as acidity, morphology, viscosity, and phase state. These new mechanistic insights demonstrate that changes in SO2 emissions, especially in isoprene-dominated environments, will significantly alter biogenic SOA physicochemical properties. Consequently, IEPOX/Sulfinorg will play an important role in understanding the historical climate and determining future impacts of biogenic SOA on the global climate and air quality.

The emissions, deposition, and chemistry of volatile organic compounds (VOCs) are thought to be influenced by underlying landscape heterogeneity at intermediate horizontal scales of several hundred meters across different forest subtypes within a tropical forest. Quantitative observations and scientific understanding at these scales, however, remain lacking, in large part due to a historical absence of canopy access and suitable observational approaches. Herein, horizontal heterogeneity in VOC concentrations in the near-canopy atmosphere was examined by sampling from an unmanned aerial vehicle (UAV) flown horizontally several hundred meters over the plateau and slope forests in central Amazonia during the morning and early afternoon periods of the wet season of 2018. Unlike terpene concentrations, the isoprene concentrations in the near-canopy atmosphere over the plateau forest were 60% greater than those over the slope forest. A gradient transport model constrained by the data suggests that isoprene emissions differed by 220 to 330% from these forest subtypes, which is in contrast to a 0% difference implemented in most present-day biosphere emissions models (i.e., homogeneous emissions). Quantifying VOC concentrations, emissions, and other processes at intermediate horizontal scales is essential for understanding the ecological and Earth system roles of VOCs and representing them in climate and air quality models.

Volatile organic compounds (VOCs) play a central role in atmospheric chemistry. In this work, VOCs in the Botanical Garden of Rio de Janeiro were determined using the TO-15 Method. The park occupies 1,370,000 m in the southern area of the city and is next to the Tijuca Forest, which is considered the largest secondary urban forest in the world. The total VOC concentrations ranged from 43.52 to 168.75 µg m, depending on the sampling site and dates. In terms of concentration isoprene represented 4 %-14 % of the total VOC masses. The results suggested that the differences in biomass, distance from the street and activities within the park affected the concentrations of VOCs. The ratios of isoprene/aromatic compounds were higher than those determined in other areas of the city, confirming that the atmosphere of this green area has the contribution of other sources. Kinetic and mechanistic reactivities were also evaluated.

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