Wintertime Formation of Large Sulfate Particles in China and Implications for Human Health.

Outdoor air pollution causes millions of premature deaths annually worldwide. Sulfate is a major component of particulate pollution. Winter sulfate observations in China show both high concentrations and an accumulation mode with a modal size >1 µm. However, we find that this observed size distribution cannot be simulated using classical gaseous and aqueous phase formation (CSF) or proposed aerosol-processing formation (APF) mechanisms. Specifically, the CSF simulation underestimates sulfate concentrations by 76% over megacities in China and predicts particle size distributions with a modal size of ∼0.35 µm, significantly smaller than observations. Although incorporating the APF mechanism in the atmospheric chemical model notably improves sulfate concentration simulation with reasonable parameters, the simulated sulfate particle size distribution remains similar to that using the CSF mechanism. We further conduct theoretical analyses and show that particles with diameters <0.3 µm grow rapidly (2-3 s) to 1 µm through the condensation of sulfuric acid in fresh high-temperature exhaust plumes, referred to as in-source formation (ISF). An ISF sulfate source equivalent to 15% of sulfur emissions from fossil fuel combustion largely explains both observed size distributions and mass concentrations of sulfate particles. The findings imply that ISF is a major source of wintertime micron-sized sulfate in China and underscore the importance of considering the size distribution of aerosols for accurately assessing the impacts of inorganic aerosols on radiative forcing and human health.

Potassium-doped g-C3N4 enables efficient visible-light-driven dye degradation.

Element doping is recognized as an efficient method to boost the photocatalytic performance of photocatalysts. Here, a new potassium ion-doped precursor, potassium sorbate, was employed in melamine configuration during calcination process to prepare the potassium-doped g-C3N4 (KCN). By various characterization techniques and electrochemical measurements, the doping of K in g-C3N4 can efficiently modify the band structure to enhance the light absorption and greatly increase the conductivity to accelerate charge transfer and photogenerated carrier separation, ultimately achieving an excellent photodegradation of the organic pollutant (methylene blue, MB). These results have demonstrated that the approach of potassium incorporation in g-C3N4 has potential in fabricating high-performance photocatalysts for organic pollutant removal.

Ambient observations indicating an increasing effectiveness of ammonia control in wintertime PM2.5 reduction in Central China.

Ammonia emission reduction is increasingly being considered one of the control measures to mitigate wintertime fine particulate matter (PM2.5) pollution. Three wintertime observations from 2012 to 2018 in Wuhan, China, were analyzed to examine the effectiveness of ammonia control in wintertime PM2.5 reduction based on the critical total ammonia concentration (CTAC, i.e., the inflection point of effective ammonia control for PM2.5 mass reduction based on the asymmetric response of PM2.5 to ammonia control). The CTAC gradually approached 0% (immediate effectiveness), with values of -26% in 2012, -23% in 2015, and -9% in 2018. At the observed ambient conditions, there were significant positive correlations of the CTAC with sulfate and total nitrate changes, in contrast to the negative correlation of the CTAC with total ammonia change. An approximately 10% total ammonia reduction could offset the decline in CTAC attributed to a 30-40% sulfate or 20-30% total nitrate reduction in Wuhan. This study indicates that the combined control of SO2 + NOx (NO+NO2) remains the preferred way to reduce inorganic particles in Central China at present, despite a tendency of the ambient chemical state moving towards effective ammonia control. However, as the CTAC approaches 0%, the effectiveness of ammonia and NOx reduction measures targeting wintertime PM2.5 can greatly exceed that observed during the 2012-2018 period in Central China.