Summertime ozone formation in Xi'an and surrounding areas, China

Abstract

Abstract. In this study, the ozone (O 3 ) formation in China's northwest city of Xi'an and surrounding areas is investigated using the Weather Research and Forecasting atmospheric chemistry (WRF-Chem) model during the period from 22 to 24 August 2013, corresponding to a heavy air pollution episode with high concentrations of O 3 and PM 2.5 . The model generally performs well compared to measurements in simulating the surface temperature, relative humidity, and wind speed and direction, near-surface O 3 and PM 2.5 mass concentrations, and aerosol constituents. High aerosol concentrations in Xi'an and surrounding areas significantly decrease the photolysis frequencies and can reduce O 3 concentrations by more than 50 µg m −3 (around 25 ppb) on average. Sensitivity studies show that the O 3 production regime in Xi'an and surrounding areas is complicated, varying from NO x to VOC (volatile organic compound)-sensitive chemistry. The industrial emissions contribute the most to the O 3 concentrations compared to biogenic and other anthropogenic sources, but neither individual anthropogenic emission nor biogenic emission plays a dominant role in the O 3 formation. Under high O 3 and PM 2.5 concentrations, a 50 % reduction in all the anthropogenic emissions only decreases near-surface O 3 concentrations by about 14 % during daytime. The complicated O 3 production regime and high aerosol levels pose a challenge for O 3 control strategies in Xi'an and surrounding areas. Further investigation regarding O 3 control strategies will need to be performed, taking into consideration the rapid changes in anthropogenic emissions that are not reflected in the current emission inventories and the uncertainties in the meteorological field simulations.

Effects of photochemical oxidation on the mixing state and light absorption of black carbon in the urban atmosphere of China

“…Characterization of OX Significant variations in the time-resolved (5 min averages) in OX were observed over the entire campaign periods at both Beijing and Xi'an, with mixing ratios ranging from 19 to 79 ppb and 10 to 60 ppb and averaging 40 ± 11 ppb and 25 ± 10 ppb at the two sites, respectively (supplemental figure S2). Differences in the daily levels of O 3 precursor gases (NO x ) and volatile organic compounds (VOCs) as well as the O 3 -NO x -VOCs coupled chemistry presumably were the main factors influencing the variations in the day-to-day OX values (Tang et al 2012, Feng et al 2016. Although O 3 contributed only ∼30% to the OX at both sites on average, the O 3 /OX ratios increased to ∼50% in the afternoon when OX reached its daily maximum.…”

Aerosol–radiation feedback deteriorates the wintertime haze in the North China Plain

“…A persistent air pollution episode from 5 December 2015 to 4 January 2016 in the NCP is simulated using the WRF-Chem model. During the study episode, the average hourly [PM 2.5 ] in the NCP are approximately 127.9 µg m −3 , within the fourth grade of National Ambient Air Quality Standards with [PM 2.5 ] between 115 and 150 µg m −3 (moderately polluted, Feng et al, 2016). The persistent and widespread haze pollution episode with high [PM 2.5 ] in the NCP provides a suitable case for observation analyses and model simulations to investigate the ARF effect on haze pollution.…”

“…Based on field measurements, recent studies have proposed that the high level of PM 2.5 increases the stability of PBL due to ARF and further decreases the PBL height (PBLH), consequently enhancing PM 2.5 concentrations ([PM 2.5 ]) (Quan et al, 2013;Petäjä et al, 2016;Yang et al, 2016;Tie et al, 2017;. Online-coupled meteorology and chemistry models have also been used to verify the impact of ARF on the PBLH and near-surface [PM 2.5 ] during haze episodes in Europe, eastern China, and northern China (Forkel et al, 2012;Z. F. Wang et al, 2014;Wang et al, 2015;Gao et al, 2015).…”

Spatiotemporal Distribution of PM2.5 and O3 and Their Interaction During the Summer and Winter Seasons in Beijing, China

“…In fact, although many studies have reported on PM 2.5 and O 3 pollution, most of them focused on spatiotemporal distribution and their relationships with weather conditions; research on the interaction of PM 2.5 and O 3 in the atmosphere is still rare. Feng et al [37] pointed out that high aerosol concentrations can significantly decrease photolysis frequencies and reduce O 3 concentration by more than 50 µg/m 3 in the summertime. In addition, previous studies also reported a significant positive correlation between PM 2.5 and O 3 concentrations during the summertime [38,39].…”