Distinct particle modes in the lower stratosphere constrain secondary aerosol chemistry and gas-phase concentrations

<p>There are distinct types of aerosol particles in the lower stratosphere. Stratospheric sulfuric acid particles with and without meteoric metals coexist with mixed organic-sulfate particles that originated in the troposphere. That these particles remain distinct has important implications for aerosol chemistry and the concentrations of several gas-phase species. Neither semi-volatile organics nor ammonia can be in equilibrium with the gas phase. The gas-phase concentrations of semi-volatile organics and ammonia must be very low, or else the sulfuric acid particles would not stay so pure. The upper concentration limits are around a pptv. Yet the sulfuric acid particles in the Northern Hemisphere show a very small but measurable uptake of organics and ammonia, indicating non-zero gas-phase concentrations of those species. Finally, the organic-sulfate particles must be resistant to photochemical loss, or else they would no longer retain their organic content.</p>

Rising Importance of Organosulfur Species for Aerosol Properties and Future Air Quality

<div>Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), a key isoprene oxidation product, with inorganic sulfate aerosol yields substantial amounts of secondary organic aerosol (SOA) through the formation of organosulfur. The extent and implications of inorganic-to-organic sulfate conversion, however, are unknown. Herein, we reveal that extensive consumption of inorganic sulfate occurs, which increases with the IEPOX-to-inorganic sulfate ratio (IEPOX:Sulf_inorg), as determined by laboratory and field measurements. We further demonstrate that organosulfur greatly modifies critical aerosol properties, such as acidity, morphology, viscosity, and phase state. These new mechanistic insights reveal that changes in SO₂ emissions, especially in isoprene-dominated environments, will significantly alter biogenic SOA physicochemical properties. Consequently, IEPOX:Sulf_inorg will play a central role in understanding historical climate and determining future impacts of biogenic SOA on global climate and air quality.</div>

Rising Importance of Organosulfur Species for Aerosol Properties and Future Air Quality

<div>Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), a key isoprene oxidation product, with inorganic sulfate aerosol yields substantial amounts of secondary organic aerosol (SOA) through the formation of organosulfur. The extent and implications of inorganic-to-organic sulfate conversion, however, are unknown. Herein, we reveal that extensive consumption of inorganic sulfate occurs, which increases with the IEPOX-to-inorganic sulfate ratio (IEPOX:Sulf_inorg), as determined by laboratory and field measurements. We further demonstrate that organosulfur greatly modifies critical aerosol properties, such as acidity, morphology, viscosity, and phase state. These new mechanistic insights reveal that changes in SO₂ emissions, especially in isoprene-dominated environments, will significantly alter biogenic SOA physicochemical properties. Consequently, IEPOX:Sulf_inorg will play a central role in understanding historical climate and determining future impacts of biogenic SOA on global climate and air quality.</div>

Organosulfates in aerosols downwind of an urban region in central Amazon

Aerosols in the central Amazon downwind of a city contain considerable concentrations of organic sulfate derived from isoprene, correlating with inorganic aerosol sulfate.

Aerosol physicochemical properties and implications for visibility during an intense haze episode during winter in Beijing

The evolution of physical, chemical and optical properties of urban aerosol particles was characterized during an extreme haze episode in Beijing, PRC, from 24 through 31 January 2013 based on in situ measurements. The average mass concentrations of PM1, PM2.5 and PM10 were 99 ± 67 μg m−3 (average ± SD), 188 ± 128 μg m−3 and 265 ± 157 μg m−3, respectively. A significant increase in PM1-2.5 fraction was observed during the most heavily polluted period. The average scattering coefficient at 550 nm was 877 ± 624 Mm−1. An increasing relative amount of coarse particles can be deduced from the variations of backscattering ratios, asymmetry parameter and scattering Ångström exponent. Particle number-size distributions between 14 and 2500 nm diameter showed high number concentrations, particularly in the nucleation mode and accumulation mode. Size-resolved chemical composition of submicron aerosol from a high-resolution time-of-flight aerosol mass spectrometer showed that the mass concentrations of organic, sulfate, nitrate, ammonium and chlorine mainly resided on particles between 500 and 800 nm (vacuum diameter), and nitrate and ammonium contributed greatly to particle growth during the heavily polluted day (28 January). Increasing relative humidity and stable synoptic conditions on 28 January combined with heavy pollution on 28 January, leading to enhanced water uptake by the hygroscopic submicron particles and formation of secondary aerosol, which might be the main reasons for the severity of the haze episode. Light-scattering apportionment showed that organic, sulfate, ammonium nitrate and ammonium chloride compounds contributed to light-scattering fractions of 54, 24, 12 and 10%, respectively. This study indicated that the organic component in submicron aerosol played an important role in visibility degradation during the haze episode in Beijing.