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The Asian Summer Monsoon Anticyclone (AMA) is known to bring ground-level pollutants up to the stratosphere. Aerosols in the AMA often form what is known as the Asian Tropopause Aerosol Layer (ATAL), with modelling studies suggesting that the ATAL can provide up to 15 % of the stratospheric aerosol in the Northern Hemisphere. In this work, we present single-particle mass spectrometry measurements of aerosol composition in the AMA outflow and in the North American upper troposphere/lower stratosphere (UTLS) during the same season. Measurements were taken by the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument and made during the Asian Summer Monsoon Chemical & CLimate Impact Project (ACCLIP). We find that the dominant aerosol type found in the ATAL and those found in the UTLS over North America are chemically different. Despite high concentrations of ground-level gas phase pollutants, particles in the ATAL are dominated by secondary nitrate particles. The organic content of these particles is low, which precludes them from being organic-nitrate aerosol; thus, we believe that these particles are either nitric/sulfuric acid solutions, or they are mixtures of partially neutralized ammonium nitrate/sulfate. Finally, we present the mass concentrations of nitrate particles, dust, and sulfate-organic particles in the ATAL, and estimate each particle type’s influence on the aerosol composition over the North American continent.

Biomass burning is a significant contributor to atmospheric pollution, its emissions have been found to have adverse impacts on climate and human health. Largely, these impacts are dictated by how the composition of the emissions changes once emitted into the atmosphere. Recently, anhydrides have been identified as a significant fraction of biomass burning emissions, however, little is known about their atmospheric evolution, or their interactions within the burn plume. Without this understanding, it is challenging to predict the impact of anhydrides on biomass burning emissions, and by extension, their influence on climate and health. In this study, we investigate anhydrides as potentially unrecognized electrophiles in the atmosphere. Firstly, by exploring their reactivity towards important biomass burning emitted nucleophiles, and secondly, by measuring their uptake on the emissions themselves. Our results show that phthalic and maleic anhydride can react with a wide range of nucleophiles, including hydroxy and amino-containing compounds, such as levoglucosan or aniline. Additionally, using a coated-wall flow tube setup, we demonstrate that anhydrides reactively uptake to biomass burning films and influence their composition. The anhydride nucleophile reaction was found to be irreversible, proceeding without sunlight or free radicals and indicating it may occur during the day or night time. Furthermore, the reaction products were found to be water-stable and contain functional groups which enhance their mass and likely contribute to the formation of secondary organic aerosol, with knock-on climate effects. Overall, our study sheds light on the fundamental chemistry of anhydrides and their potential impacts in the atmosphere.

We determine, for the first time, the reactivity of ground brake pads with ozone and discuss the potential impact of this interaction on urban air quality.

In this study, we report the heterogeneous chemistry of ozone with urban road dust and anti-icer. We present a novel pathway for chlorine activation during ozone uptake by anti-icer and discuss its potential air quality impacts in cold-climate urban regions.

The billions of tons of mineral dust released into the atmosphere each year provide an important surface for reaction with gas-phase pollutants. These reactions, which are often enhanced in the presence of light, can change both the gas-phase composition of the atmosphere and the composition and properties of the dust itself. Because dust contains titanium-rich grains, studies of dust photochemistry have largely employed commercial titanium dioxide as a proxy for its photochemically active fraction; to date, however, the validity of this model system has not been empirically determined. Here, for the first time, we directly investigate the photochemistry of the complement of natural titanium-containing minerals most relevant to mineral dust, including anatase, rutile, ilmenite, titanite, and several titanium-bearing species. Using ozone as a model gas-phase pollutant, we show that titanium-containing minerals other than titanium dioxide can also photocatalyze trace gas uptake, that samples of the same mineral phase can display very different reactivity, and that prediction of dust photoreactivity based on elemental/mineralogical analysis and/or light-absorbing properties is challenging. Together, these results show that the photochemistry of atmospheric dust is both richer and more complex than previously considered, and imply that a full understanding of the scope and impact of dust-mediated processes will require the community to engage with this complexity via the study of ambient mineral dust samples from diverse source regions.

Although organosulfates (ROSO3–) comprise a significant component of secondary organic aerosol (SOA) mass, their atmospheric formation mechanisms are not fully understood. Here, using methacrolein as a model organosulfate precursor, we present a new, mineral-mediated photochemical pathway for organosulfate formation. First, we describe studies of TiO2-catalyzed formation of the atmospherically important organosulfate hydroxyacetone sulfate from methacrolein as a function of illumination time, catalyst loading, sulfate concentration, counterion identity, and methacrolein concentration. Then, we propose a sulfate radical-mediated mechanism for organosulfate formation consistent with these observations. Finally, we show that natural Ti-containing minerals and road dust not only catalyze the formation of comparable amounts of hydroxyacetone sulfate to those formed in the presence of commercial TiO2 but also facilitate the production of additional organosulfate species. These results highlight the complex natu...