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The Community Multiscale Air Quality model (CMAQv5.2) was implemented to investigate the sources and sinks of oxygenated volatile organic compounds (OVOCs) during a high O

The COVID-19 outbreak greatly limited human activities and reduced primary emissions particularly from urban on-road vehicles but coincided with Beijing experiencing “pandemic haze,” raising the public concerns about the effectiveness of imposed traffic policies to improve the air quality. This paper explores the relationship between local vehicle emissions and the winter haze in Beijing before and during the COVID-19 lockdown based on an integrated analysis framework, which combines a real-time on-road emission inventory, in situ air quality observations, and a localized numerical modeling system. We found that traffic emissions decreased substantially during the COVID-19 pandemic, but its imbalanced emission abatement of NOx (76%, 125.3 Mg/day) and volatile organic compounds (VOCs, 53%, 52.9 Mg/day) led to a significant rise of atmospheric oxidants in urban areas, resulting in a modest increase in secondary aerosols due to inadequate precursors, which still offset reduced primary emissions. Moreover, the enhanced oxidizing capacity in the surrounding regions greatly increased the secondary particles with relatively abundant precursors, which was transported into Beijing and mainly responsible for the aggravated haze pollution. We recommend that mitigation policies should focus on accelerating VOC emission reduction and synchronously controlling regional sources to release the benefits of local traffic emission control.

Atmospheric glyoxal (GLY) and methylglyoxal (MGLY) are key precursors of secondary organic aerosol (SOA). However, anthropogenic emissions of GLY and MGLY and their contribution to surface GLY and MGLY concentrations, as well as the secondary organic aerosol (SOA) formation, are not well quantified. By developing an emission inventory of anthropogenic GLY and MGLY and improving the Community Multiscale Air Quality Model (CMAQ) with SOA formation from irreversible surface uptake of GLY and MGLY, as well as a precursor-origin resolved technique, we quantified the source contributions of GLY and MGLY and their impact on wintertime SOA formation in Beijing, China. The total emissions of GLY and MGLY in Beijing in 2017 are 1.1 × 104 kmol and 7.0 × 103 kmol, respectively. Anthropogenic primary emissions are found to be the dominant contributor to wintertime GLY and MGLY concentrations (∼74% for GLY and ∼63% for MGLY). Anthropogenic primary emissions of GLY and MGLY contributes to 30% of GLY/MGLY SOA daily average concentration and accounts for up to 45% of nighttime GLY/MGLY SOA in winter. The study suggests that the anthropogenic GLY and MGLY emissions, mainly from gasoline vehicles and cooking, are important for SOA formation and shall be strictly controlled in Chinese megacities.

An improved three-regime (3R) O3 attribution technique for O3 source apportionment in regional chemical transport models is developed to divide the entire range of VOC-NO x-O3 formation sensitivity to VOC-limited, transition, and NO x-limited regimes based on the value of a regime indicator R. The threshold R values to mark the start ( Rts) and end ( Rte) of the transition regime are defined at the point where O3-NO x sensitivity turns from negative to positive and where O3-NO x sensitivity is ten times higher than O3-VOC sensitivity, respectively. Rts and Rte are determined using NO x and VOC sensitivity simulations in a box model with a modified SAPRC-11 mechanism. For the widely used indicator ration R = ( PH2O2 + PROOH)/ PHNO3, which is based on the production rates of H2O2, HNO3 and organic hydroperoxides (ROOH), the recommended Rts and Rte values are 0.047 and 5.142, respectively. Parameterized attribution functions, depending only on the values of R, are developed to apportion modeled in situ O3 formation in the transition regime to NO x and VOCs. The new 3R and the traditional two-regime (2R) schemes are incorporated into the Community Multiscale Air Quality (CMAQ) model to quantify NO x and VOC contributions to regional O3 concentrations in China in August 2013. The 3R approach predicts approximately 5-10 ppb and up to 15 ppb higher NO x contributions to 8 h O3 in in the North China Plain, the Yangtze River Delta and the Pearl River Delta than the 2R approach. The big differences in O3 attribution between 2R and 3R can have significant policy implications for air pollution emission controls.

The University of California-Davis_Primary (UCD_P) model was applied to simultaneously track ∼ 900 source contributions to primary particulate matter (PM) in California for seven continuous years (January 1st, 2000 to December 31st, 2006). Predicted source contributions to primary PM2.5 mass, PM1.8 elemental carbon (EC), PM1.8 organic carbon (OC), PM0.1 EC, and PM0.1 OC were in general agreement with the results from previous source apportionment studies using receptor-based techniques. All sources were further subjected to a constraint check based on model performance for PM trace elemental composition. A total of 151 PM2.5 sources and 71 PM0.1 sources contained PM elements that were predicted at concentrations in general agreement with measured values at nearby monitoring sites. Significant spatial heterogeneity was predicted among the 151 PM2.5 and 71 PM0.1 source concentrations, and significantly different seasonal profiles were predicted for PM2.5 and PM0.1 in central California vs southern California. Population-weighted concentrations of PM emitted from various sources calculated using the UCD_P model spatial information differed from the central monitor estimates by up to 77% for primary PM2.5 mass and 148% for PM2.5 EC because the central monitor concentration is not representative of exposure for nearby population. The results from the UCD_P model provide enhanced source apportionment information for epidemiological studies to examine the relationship between health effects and concentrations of primary PM from individual sources.

This research investigated the effectiveness of phosphate rocks in immobilizing Pb from aqueous solutions and contaminated soils. Different amounts of phosphate rocks were reacted with aqueous solutions containing Pb or with Pb-contaminated soils. The results show that phosphate rocks were effective in immobilizing Pb from aqueous solutions with a minimum Pb removal of 38.8-100%. The reaction time had less effect on Pb immobilization than the quantity of phosphate rocks used. Selected phosphate rocks reduced water-soluble Pb from a contaminated soil by 56.8-100%. The primary mechanism of Pb immobilization was via dissolution of phosphate rocks and precipitation of a fluoropyromorphite-like mineral. Different methods of mixing phosphate rocks and soil and incubation time had little effect on Pb immobilization. Our results strongly demonstrate that phosphate rocks may provide a cost-effective way to remediate Pb-contaminated water, soils, and wastes.

Remediation of Pb-contaminated wastes has received considerable attention recently. We have previously shown that hydroxyapatite [Ca 5 (PO 4 ) 3 OH] can reduce Pb 2+ concentrations below the EPA action level (72.4 nmol L -1 ) and, thus, has the potential for in situ Pb 2+ immobilization against leaching. This research investigated the effects of NO 3 - , Cl - , F - , SO 4 2- , and CO 3 2- on hydroxyapatite-Pb 2+ interactions. Solutions containing initial Pb 2+ concentrations of 24.1-482 μmol L -1 were reduced to below 72.4 nmol L -1 after reaction with hydroxyapatite, except in the presence of high levels of CO 3 2- and Pb 2+

Lead contamination is of environmental concern due to its effect on human health. The purpose of this study was to develop a technology to immobilize Pb in situ in contaminated soils and wastes using apatite. Hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] was reacted with aqueous Pb, resin-exchangeable Pb, and Pb-contaminated soil material. The effectiveness of natural apatite to attenuate Pb was also tested. Hydroxyapatite reduced initial Pb concentrations of 5-500 mg L -1 to 0.18-19.7 μg L -1 . Aqueous Pb in Pb-contaminated soil materials was reduced from 2273 to 36 μg L -1 after reaction with hydroxyapatite. We hypothesize that Pb was immobilized by dissolution of hydroxyapatite and precipitation of hydroxypyromorphite [Pb 10 (PO 4 ) 6 (OH) 2 ]