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Long-term observations show that a rising fraction of ammonium nitrate in PM_2.5 reduces aerosol acidity, suppressing the heterogeneous conversion from NO₂ to HONO. This weakens its contribution to the HONO source and atmospheric oxidation capacity.

Second-generation oxidation boosts the production of anthropogenic organic aerosol, according to an analysis of urban haze in an experimental chamber.

Experiments performed in the CERN CLOUD chamber show that, under upper-tropospheric conditions, new atmospheric particle formation may be initiated by the reaction of hydroxyl radicals with isoprene emitted by rainforests.

Secondary organic aerosols in Beijing are driven by emissions from outside of the city, with seasonally different emission sources, according to molecular chemical characterization of particulate air pollution.

Uncertainties in the absorptive properties of black and brown carbon particles limit our understanding of their warming potential. Following an extensive field campaign, Liuet al. report that the magnitude of warming is dependent on particle coatings, which vary due to source and photochemical aging.

The formation of secondary organic aerosol in Chinese megacities is dominated by the condensation of anthropogenic organic vapours, according to measurements across three urbanized regions.

Atmospheric aerosol particles can significantly influence the climate system. Analyses of observations and observation-based modelling data reveal that biogenic aerosol emissions soar in response to warming, exerting a cooling effect in a negative feedback loop.

Analyses of atmospheric nitrogen chemistry in Beijing’s air pollution during the COVID-19 lockdown suggest an increasing role of nighttime nitrogen chemistry in haze formation above the city.

Atmospheric organic compounds are central to key chemical processes that influence air quality. Concurrent measurements of a wide range of these compounds, including previously unmeasured ones, provide closure on OH reactivity.

Field data from an iodine-rich, coastal environment point to the molecular steps involved in the formation of new aerosol particles from iodine vapours over coastal regions.

Secondary organic aerosol (SOA) particles can scatter radiation and act as cloud condensation nuclei, and thereby influence the Earth's radiation balance. It is generally assumed that SOA particles are liquid, but these authors show that they can adopt an amorphous solid state under ambient conditions. The findings challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere.

Iodic acid (HIO₃) forms aerosols very efficiently, but its gas-phase formation mechanism is not well understood. Atmospheric simulation chamber experiments, quantum chemical calculations and kinetic modelling have now revealed that HIO₃ forms as an early iodine oxidation product from hypoiodite. The mechanism explains field measurements and suggests a catalytic role for iodine in particle formation.

Nitrogen monoxide at low concentrations can promote the formation of highly oxygenated organic molecules, which are crucial precursors to secondary organic aerosol (SOA), rather than inhibit it as traditionally thought.

Organic aerosol particles are important to climate and human health but remain poorly characterized on account of their immense chemical complexity. Here, using both field and laboratory measurements of organic aerosol, we demonstrate the use of average carbon oxidation state for describing aerosol chemical properties and atmospheric transformations.

By performing experiments under upper tropospheric conditions, nitric acid, sulfuric acid and ammonia can form particles synergistically, at rates orders of magnitude faster than any two of the three components.

Nearly all organic carbon has now been quantified and characterized in a highly complex evolving atmospheric system, specifically, the multigenerational oxidation of α-pinene. It has been observed that initial addition of functional groups quickly gives way to fragmentation reactions, with organic carbon ultimately becoming sequestered in chemically resistant reservoirs: organic aerosols and long-lived gas-phase species.

Forests emit compounds into the atmosphere that are oxidized into highly oxygenated molecules that serve as precursors for cloud condensation nuclei–a process that impacts the climate, but is poorly represented in models. Here the authors create a new model that accurately depicts highly oxygenated molecule and climate dynamics over Boreal forests.

Measurements in the CLOUD chamber at CERN show that the rapid condensation of ammonia and nitric acid vapours could be important for the formation and survival of new particles in wintertime urban conditions, contributing to urban smog.

The growth rates of freshly formed aerosol particles influence what fraction of these can reach sizes large enough to affect cloud formation and climate. Here, the authors show that the nano-particle growth in a sulphuric acid containing system can be enhanced by the presence of ions or small acid-base clusters.

The growth of the smallest atmospheric particles to sizes at which they may act as seeds for cloud droplets is a key step linking aerosols to clouds and climate. A synthesis of research indicates that the mechanisms controlling this growth depend on the size of the growing particle.

Aerosol particles can form in the atmosphere by nucleation of highly oxidized biogenic vapours in the absence of sulfuric acid, with ions from Galactic cosmic rays increasing the nucleation rate by one to two orders of magnitude compared with neutral nucleation.

The link between biogenic volatile organic compounds in the atmosphere and their conversion to aerosol particles is unclear, but a direct reaction pathway is now described by which volatile organic compounds lead to low-volatility vapours that can then condense onto aerosol surfaces, producing secondary organic aerosol.

The growth of nucleated organic particles has been investigated in controlled laboratory experiments under atmospheric conditions; initial growth is driven by organic vapours of extremely low volatility, and accelerated by more abundant vapours of slightly higher volatility, leading to markedly different modelled concentrations of atmospheric cloud condensation nuclei when this growth mechanism is taken into account.

Amines at typical atmospheric concentrations of a only few molecules per trillion air molecules combine with sulphuric acid to form highly stable aerosol particles at rates similar to those observed in the lower atmosphere.

The CLOUD experiment provides important insights into new particle formation in different atmospheric environments.

Boreal wetlands emit terpenes which initiate atmospheric new particle formation to an even greater degree than is usually seen over boreal forests, according to direct measurements of volatile organic compounds from a Finnish wetland.