Anisotropic diffusion of volatile pollutants at air-water interface

The volatile pollutants that spill into natural waters cause water pollution. Air pollution arises from the water pollution because of volatilization. Mass exchange caused by turbulent fluctuation is stronger in the direction normal to the air-water interface than in other directions due to the large density difference between water and air. In order to explore the characteristics of anisotropic diffusion of the volatile pollutants at the air-water interface, the relationship between velocity gradient and mass transfer rate was established to calculate the turbulent mass diffusivity. A second-order accurate smooth transition differencing scheme （STDS） was proposed to guarantee the boundedness for the flow and mass transfer at the air-water interface. Simulations and experiments were performed to study the trichloroethylene （C2HC13） release. By comparing the anisotropic coupling diffusion model, isotropic coupling diffusion model, and non-coupling diffusion model, the features of the transport of volatile pollutants at the air-water interface were determined. The results show that the anisotropic coupling diffusion model is more accurate than the isotropic coupling diffusion model and non-coupling diffusion model. Mass transfer significantly increases with the increase of the air-water relative velocity at a low relative velocity. However, at a higher relative velocity, an increase in the relative velocity has no effect on mass transfer.

Chemical characteristics of PM_(2.5) during dust storms and air pollution events in Chengdu,China

Daily fine particulate （PM2.5） samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms （DSs） and several types of pollution events, including haze （HDs）, biomass burning （BBs）, and fireworks displays （FDs）. The highest PM2.5 mass concentrations were found during DSs （283.3 μg/m^3）, followed by FDs （212.7 μg/m^3）, HDs （187.3 μg/m^3 ）, and BBs （130.1 μ g/m^3）. The concentrations of most elements were elevated during DSs and pollution events, except for BBs. Secondary inorganic ions （NO3^- , SO4^2-, and NH4^＋） were enriched during HDs, while PM2.5 from BBs showed high K^＋ but low SO4^2- , FDs caused increases in K^＋ and enrichment in SO4^2-. Ca^2＋. was abundant in DS samples, Ion-balance calculations indicated that PM2.5 from HDs and FDs was more acidic than on normal days, but DS and BB particles were alkaline. The highest organic carbon （OC） concentration was 26.1 μg/m^3 during FDs, followed by BBs （23.6 μg/m^3 ）, HDs （19.6 μg/m^3 ）, and DSs （18.8 μg/m^3 ）. In contrast, elemental carbon （EC） concentration was more abundant during HDs （10.6μg/m^3） and FDs （9.5 μg/m^3） than during BBs （6.2μg/m^3） and DSs （6.0 μg/m^3）. The highest OC/EC ratios were obtained during BBs, with the lowest during HDs. SO4^2＋ /K^＋ and TCA/SO4^2- ratios proved to be effective indicators for differentiating pollution events. Mass balance showed that organic matter, SO4^2-, and NO3^- were the dominant chemical components during pollution events, while soil dust was dominant during DSs.

Measurement of hydrogen peroxide and organic hydroperoxide concentrations during autumn in Beijing, China

Gaseous peroxides play important roles in atmospheric chemistry. To understand the pathways of the formation and removal of peroxides, atmospheric peroxide concentrations and their controlling factors were measured from 7：00 to 20：00 in September, October, and November 2013 at a heavily trafficked residential site in Beijing, China, with average concentrations of hydrogen peroxide（H2O2） and methyl hydroperoxide（MHP） at 0.55 ppb and 0.063 ppb, respectively. H2O2 concentrations were higher in the afternoon and lower in the morning and evening, while MHP concentrations did not exhibit a regular diurnal pattern. Both H2O2 and MHP concentrations increased at dusk in most cases. Both peroxides displayed monthly variations with higher concentrations in September. These results suggested that photochemical activity was the main controlling factor on variations of H2O2 concentrations during the measurement period. Increasing concentrations of volatile organic compounds emitted by motor vehicles were important contributors to H2O2 and MHP enrichment. High levels of H2O2 and MHP concentrations which occurred during the measurement period probably resulted from the transport of a polluted air mass with high water vapor content passing over the Bohai Bay, China.

Characteristics of atmospheric single particles during haze periods in a typical urban area of Beijing：A case study in October,2014

To investigate the composition and possible sources of particles, especially during heavy haze pollution, a single particle aerosol mass spectrometer（SPAMS） was deployed to measure the changes of single particle species and sizes during October of 2014, in Beijing. A total of 2,871,431 particles with both positive and negative spectra were collected and characterized in combination with the adaptive resonance theory neural network algorithm（ART-2a）. Eight types of particles were classified： dust particles（dust, 8.1%）, elemental carbon（EC, 29.0%）, organic carbon（OC, 18.0%）, EC and OC combined particles（ECOC, 9.5%）,Na-K containing particles（Na K, 7.9%）, K-containing particles（K, 21.8%）, organic nitrogen and potassium containing particles（KCN, 2.3%）, and metal-containing particles（metal,3.6%）. Three haze pollution events（P1, P2, P3） and one clean period（clean） were analyzed,based on the mass and number concentration of PM_（2.5）and the back trajectory results from the hybrid single particle Lagrangian integrated trajectory model（Hysplit-4 model）. Results showed that EC, OC and K were the major components of single particles during the three haze pollution periods, which showed clearly increased ratios compared with those in the clean period. Results from the mixing state of secondary species of different types of particles showed that sulfate and nitrate were more readily mixed with carbon-containing particles during haze pollution episodes than in clean periods.