Personal exposure to PM2.5 in Chinese rural households in the Yangtze River Delta.

High levels of PM2.5 exposure and associated health risks are of great concern in rural China. For this study, we used portable PM2.5 monitors for monitoring concentrations online, recorded personal time-activity patterns, and analyzed the contribution from different microenvironments in rural areas of the Yangtze River Delta, China. The daily exposure levels of rural participants were 66 µg/m3 (SD 40) in winter and 65 µg/m3 (SD 16) in summer. Indoor exposure levels were usually higher than outdoor levels. The exposure levels during cooking in rural kitchens were 140 µg/m3 (SD 116) in winter and 121 µg/m3 (SD 70) in summer, the highest in all microenvironments. Winter and summer values were 252 µg/m3 (SD 103) and 204 µg/m3 (SD 105), respectively, for rural people using biomass for fuel, much higher than those for rural people using LPG and electricity. By combining PM2.5 concentrations and time spent in different microenvironments, we found that 92% (winter) and 85% (summer) of personal exposure to PM2.5 in rural areas was attributable to indoor microenvironments, of which kitchens accounted for 24% and 27%, respectively. Consequently, more effective policies and measures are needed to replace biomass fuel with LPG or electricity, which would benefit the health of the rural population in China.

Improving Flue Gas Mercury Removal in Waste Incinerators by Optimization of Carbon Injection Rate.

This study tested the mercury emission characteristics of six municipal solid waste incinerators (MSWIs) and recommended future mercury control via adjusting operational parameters. The results indicated that over 99% of the mercury in solid wastes ended in fly ash and flue gas, of which 3.3-66.3% was emitted to air through stack gas. Mercury in the stack gas was mainly in the form of oxidized mercury (Hg2+), the proportion (65.4-89.0%) of which was far higher than previous estimation (15%). Mercury removal efficiencies (MRE) of the tested incinerators were in the range of 33.6-95.2%. The impact of waste incineration capacity, gas flow, fly ash yield, and activated carbon (AC) injection on MRE were analyzed. We found that the MRE was significantly linearly correlated to the ratio of AC injection and fly ash yield (correlation coefficient = 0.98, significance <0.01). AC injection value is determined based on the control of dioxin emissions without considering mercury control in traditional design. To increase MRE of MSWIs, the AC injection should increase from around 100 mg·Nm-3 to 135 mg·Nm-3 for grate furnace combustor and 170 mg·Nm-3 for circulation fluidized bed combustor, so as to reach a MRE of 90%.

Significant impact of heterogeneous reactions of reactive chlorine species on summertime atmospheric ozone and free-radical formation in north China.

Heterogeneous reactions of N2O5, O3, OH, ClONO2, HOCl, ClNO2, and NO2, with chlorine-containing particles are incorporated in the Community Multiscale Air Quality (CMAQ) model to evaluate the impact of heterogeneous reactions of reactive chlorine species on ozone and free radicals. Changes of summertime ozone and free radical concentrations due to the additional heterogeneous reactions in north China were quantified. These heterogeneous reactions increased the O3, OH, HO2 and RO2 concentrations by up to 20%, 28%, 36% and 48% for some regions in the Beijing-Tianjin-Hebei (BTH) area. These areas typically have a larger amount of NOx emissions and a lower VOC/NOx ratio. The zero-out method evaluates that the photolysis of ClNO2 and Cl2 are the major contributors (42.4% and 57.6%, respectively) to atmospheric Cl in the early morning hours but the photolysis of Cl2 is the only significant contributor after 10:00 am. The results highlight that heterogeneous reactions of reactive chlorine species are important to atmospheric ozone and free-radical formation. Our study also suggests that the on-going NOx emission controls in the NCP region with a goal to reduce both O3 and secondary nitrate can also have the co-benefit of reducing the formation Cl from ClNO2 and Cl2, which may also lead to lower secondary organic aerosol formation and thus the control of summertime PM2.5 in the region.