Simulated Sensitivity of Ozone Generation to Precursors in Beijing during a High O_(3) Episode

This study uses the WRF-Chem model combined with the empirical kinetic modeling method(EKMA curve)to study the compound pollution event in Beijing that happened in 13−23 May 2017.Sensitivity tests are conducted to analyze ozone sensitivity to its precursors,and to develop emission reduction measures.The results suggest that the model can accurately simulate the compound pollution process of photochemistry and haze.When VOCs and NOx were reduced by the same proportion,the effect of O_(3)reduction at peak time was more obvious,and the effect during daytime was more significant than at night.The degree of change in ozone was peak time>daytime average.When reducing or increasing the ratio of precursors by 25%at the same time,the effect of reducing 25%VOCs on the average ozone concentration reduction was most significant.The degree of change in ozone decreased with increasing altitude,the location of the ozone maximum change shifted westward,and its range narrowed.As the altitude increases,the VOCs-limited zone decreases,VOCs sensitivity decreases,NOx sensitivity increases.The controlled area changed from near-surface VOCs-limited to high-altitude NOx-limited.Upon examining the EKMA curve,we have found that suburban and urban are sensitive to VOCs.The sensitivity tests indicate that when VOCs in suburban are reduced about 60%,the O_(3)-1h concentration could reach the standard,and when VOCs of the urban decreased by about 50%,the O_(3)-1h concentration could reach the standard.Thus,these findings could provide references for the control of compound air pollution in Beijing.

Nitrogen Dioxide and Ozone Pollution in the Chicago Metropolitan Area

Ground-level ozone is a harmful air pollutant associated with several health issues. Ozone concentrations have exceeded the National Ambient Air Quality Standards (NAAQS) in the Chicago metropolitan area on hot summer days for many years because of nitrogen oxide and volatile organic compound emissions. Annual fourth highest 8-hour ozone concentrations have been between 0.070 and 0.084 ppm at several monitoring sites in Cook county, during the 2016-2018 time period. The continuous measurement of nitrogen dioxide (NO2) and ozone (O3) was conducted in several communities in Chicago in 2017. The air pollution impacts the health of all who live in the area. The data were used to analyze correlations between the O3 distribution and its association with ambient concentrations of NO2 from transportation emissions. Higher concentrations in NO2 and O3 occurred in succession in the daytime. The diurnal variation of O3 concentration was analyzed. The daily cycle of NO2 concentration reaches a maximum in the late morning and has smaller nighttime concentrations. The daily cycle of ozone concentration reaches the maximum in the afternoon and also becomes smaller for nighttime concentrations. In addition, relationships were found between O3 and NO2. Monthly variations of ozone and NO2 are presented. Some options to reduce ozone pollution are presented.

Anthropogenic Source Contributions to Ozone Formation in the Greater Houston Area

The Houston-Galveston-Brazoria (HGB) area of Texas has historically experienced severe air pollution events with high concentrations of ozone (O3) during the summer season. This study evaluates the contribution of different anthropogenic sources to ozone formation in the HGB area. The Emission Processing System (EPS3) is used to process emission files in four different scenarios (Base case as including All emission sources (BC), All sources— Area sources (AMA), All sources—Point sources (AMP), and All sources— Mobile sources (AMM). These files are used as input in photochemical modeling with the Comprehensive Air Quality Model with Extensions (CAMx) to simulate ozone formation. The data is analyzed for daily maximum ozone concentrations and contribution of source categories at three air quality monitoring locations (La Porte Sylvan beach-C556, Houston Texas avenue-C411, and Texas city in Galveston-C683) for a study period of June 1-June 30, 2012. The contribution of the point sources to ozone formation is dominated at all three locations, followed by mobile sources and area sources on high ozone days. The relative contributions of point sources are 27.51% ± 3.53%, 21.45% ± 7.36%, and 30.30% ± 9.36%;and mobile sources are 18.27% ± 2.22%, 20.60% ± 6.89%, and 18.61% ± 7.43%;and area sources were 4.2% ± 1.65%, 5.21% ± 1.59%, and 3.72% ± 1.52% at C556, C411, and C683, respectively. These results demonstrate the importance of regulatory focus on controlling point and mobile source emissions for NAAQS attainment in the study region.

Ozone episodes during and after the 2018 Chinese National Day holidays in Guangzhou:Implications for the control of precursor VOCs

The impact of reducing industrial emissions of volatile organic compounds(VOCs)on ozone(O_(3))pollution is of wide concern particularly in highly industrialized megacities.In this study,O_(3),nitrogen oxides(NOx)and VOCs were measured at an urban site in the Pearl River Delta region during the 2018 Chinese National Day Holidays and two after-holiday periods(one with ozone pollution and another without).O_(3)pollution occurred throughout the 7-day holidays even industrial emissions of VOCswere passively reduced due to temporary factory shutdowns,and the toluene to benzene ratios dropped from∼10 during non-holidays to∼5 during the holidays.Box model(AtChem2-MCM)simulations with the input of observation data revealed that O_(3)formation was all VOC-limited,and alkenes had the highest relative incremental reactivity(RIR)during the holiday and non-holiday O_(3)episodes while aromatics had the highest RIR during the non-pollution period.Box model also demonstrated that even aromatics decreased proportionally to levels with near-zero contributions of industrial aromatic solvents,O_(3)concentrations would only decrease by less than 20%during the holiday and non-holiday O_(3)episodes and ozone pollution in the periods could not be eliminated.The results imply that controlling emissions of industrial aromatic solvents might be not enough to eliminate O_(3)pollution in the region,and more attention should be paid to anthropogenic reactive alkenes.Isoprene and formaldehyde were among the top 3 species by RIRs in all the three pollution and non-pollution periods,suggesting substantial contribution to O_(3)formation from biogenic VOCs.

Surface ozone scenario and air quality in the north-central part of India

Tropospheric pollutants including surface ozone（O3）, nitrogen dioxide（NO2）, carbon monoxide（CO） and meteorological parameters were measured at a traffic junction（78°2′ E and 27°11′ N） in Agra, India from January 2012 to December 2012. Temporal analysis of pollutants suggests that annual average mixing ratios of tropospheric pollutants were： O3— 22.97 ± 23.36 ppbV,NO2— 19.84 ± 16.71 ppb V and CO — 0.91 ± 0.86 ppm V, with seasonal variations of O3 having maximum mixing ratio during summer season（32.41 ± 19.31 ppbV）, whereas lowest was found in post-monsoon season（8.74 ± 3.8 ppbV）. O3 precursors： NO2 and CO, showed inverse relationship with O3. Seasonal variation and high O3 episodes during summer are associated with meteorological parameters such as high solar radiation, atmospheric temperature and transboundary transport. The interdependence of these variables showed a link between the daytime mixing ratios of O3 with the nighttime level of NO2. The mixing ratios of CO and NO2 showed tight correlations, which confirms the influence of vehicular emissions combined with other anthropogenic activities due to office/working hours, shallowing, and widening of boundary layer. FLEXTRA backward trajectories for the O3 episode days clearly indicate the transport from the NW and W to S/SE and SW direction at Agra in different seasons.