Air pollution in mega cities in China

Phytotoxicity of nanoparticles: Inhibition of seed germination and root growth

Sulfate aerosols exert profound impacts on human and ecosystem health, weather, and climate, but their formation mechanism remains uncertain. Atmospheric models consistently underpredict sulfate levels under diverse environmental conditions. From atmospheric measurements in two Chinese megacities and complementary laboratory experiments, we show that the aqueous oxidation of SO2 by NO2 is key to efficient sulfate formation but is only feasible under two atmospheric conditions: on fine aerosols with high relative humidity and NH3 neutralization or under cloud conditions. Under polluted environments, this SO2 oxidation process leads to large sulfate production rates and promotes formation of nitrate and organic matter on aqueous particles, exacerbating severe haze development. Effective haze mitigation is achievable by intervening in the sulfate formation process with enforced NH3 and NO2 control measures. In addition to explaining the polluted episodes currently occurring in China and during the 1952 London Fog, this sulfate production mechanism is widespread, and our results suggest a way to tackle this growing problem in China and much of the developing world.

https://www.pnas.org/content/pnas/113/48/13630.full.pdf

Persistent sulfate formation from London Fog to Chinese haze

Review of antibiotic resistance in China and its environment

. From 2006 to 2007, the daily concentrations of major inorganic water-soluble constituents, mineral aerosol, organic carbon (OC) and elemental carbon (EC) in ambient PM10 samples were investigated from 16 urban, rural and remote sites in various regions of China, and were compared with global aerosol measurements. A large difference between urban and rural chemical species was found, normally with 1.5 to 2.5 factors higher in urban than in rural sites. Optically-scattering aerosols, such as sulfate (~16%), OC (~15%), nitrate (~7%), ammonium (~5%) and mineral aerosol (~35%) in most circumstance, are majorities of the total aerosols, indicating a dominant scattering feature of aerosols in China. Of the total OC, ~55%–60% can be attributed to the formation of the secondary organic carbon (SOC). The absorbing aerosol EC only accounts for ~3.5% of the total PM10. Seasonally, maximum concentrations of most aerosol species were found in winter while mineral aerosol peaks in spring. In addition to the regular seasonal maximum, secondary peaks were found for sulfate and ammonium in summer and for OC and EC in May and June. This can be considered as a typical seasonal pattern in various aerosol components in China. Aerosol acidity was normally neutral in most of urban areas, but becomes some acidic in rural areas. Based on the surface visibility observations from 681 meteorological stations in China between 1957 and 2005, four major haze areas are identified with similar visibility changes, namely, (1) Hua Bei Plain in N. China, and the Guanzhong Plain; (2) E. China with the main body in the Yangtze River Delta area; (3) S. China with most areas of Guangdong and the Pearl River Delta area; (4) The Si Chuan Basin in S.W. China. The degradation of visibility in these areas is linked with the emission changes and high PM concentrations. Such quantitative chemical characterization of aerosols is essential in assessing their role in atmospheric chemistry and weather-climate effects, and in validating atmospheric models.

/pdf/atmospheric-aerosol-compositions-in-china-spatial-temporal-21nw523s36.pdf

Atmospheric aerosol compositions in China: spatial/temporal variability, chemical signature, regional haze distribution and comparisons with global aerosols

In the environment, microplastics are subjected to multiple aging processes; however, information regarding the impact of aging on the environmental behavior of microplastics is still lacking. This study investigated the alteration properties of polystyrene and high-density polyethylene microplastics by heat-activated K2S2O8 and Fenton treatments to improve the understanding of their long-term natural aging in aquatic environments. Our results indicated that the O/C ratio was an alternative parameter to the carbonyl index (CI) to quantitatively describe the surface alteration properties of microplastics. The correlation model of the O/C ratio or CI versus alteration time was developed and compared by natural alteration of microplastics in freshwater samples. Moreover, the regression equation of the equilibrium adsorption capacity of altered microplastics versus the O/C ratio and average size was proposed. This study is the first effort in differentiating the relationships between the alteration properties and alteration time/adsorption capacity of microplastics, which would be helpful for predicting the weathering degree and accumulation of hydrophilic antibiotics onto aged microplastics in aquatic environments. This research develops promising strategies to accelerate the aging reactions using advanced oxidation processes, which would provide further information to assess the microplastic pollution in actual environments.

New Insights into the Aging Behavior of Microplastics Accelerated by Advanced Oxidation Processes

Effect of weathering on environmental behavior of microplastics: Properties, sorption and potential risks.

Effect of aging on adsorption behavior of polystyrene microplastics for pharmaceuticals: Adsorption mechanism and role of aging intermediates.

Adsorption of tetracycline, one of the most widely used antibiotics, onto goethite was studied as a function of pH, metal cations, and humic acid (HA) over a pH range 3-10. Five background electrolyte cations (Li(+), Na(+), K(+), Ca(2+), and Mg(2+)) with a concentration of 0.01 M showed little effect on the tetracycline adsorption at the studied pH range. While the divalent heavy metal cation, Cu(2+), could significantly enhance the adsorption and higher concentration of Cu(2+), stronger adsorption was found. The results indicated that different adsorption mechanisms might be involved for the two types of cations. Background electrolyte cations hardly interfere with the interaction between tetracycline and goethite surfaces because they only form weak outer-sphere surface complexes. On the contrary, Cu(2+) could enhance the adsorption via acting as a bridge ion to form goethite-Cu(2+)-tetracycline surface complex because Cu(2+) could form strong and specific inner-sphere surface complexes. HA showed different effect on the tetracycline sorption under different pH condition. The presence of HA increased tetracycline sorption dramatically under acidic condition. Results indicated that heavy metal cations and soil organic matters have great effects on the tetracycline mobility in the soil environment and eventually affect its exposure concentration and toxicity to organisms.

Shixiang Gao

Papers

New Insights into the Aging Behavior of Microplastics Accelerated by Advanced Oxidation Processes

Effect of weathering on environmental behavior of microplastics: Properties, sorption and potential risks.

Effect of aging on adsorption behavior of polystyrene microplastics for pharmaceuticals: Adsorption mechanism and role of aging intermediates.

Adsorption of tetracycline onto goethite in the presence of metal cations and humic substances

Adsorption of tetracycline (TC) onto montmorillonite: Cations and humic acid effects