Impacts of biogenic and anthropogenic emissions on summertime ozone formation in the Guanzhong Basin, China

Abstract

Abstract. This study is the first attempt to understand the synergistic impact of anthropogenic and biogenic emissions on summertime ozone (O3) formation in the Guanzhong (GZ) Basin where Xi'an, the oldest and the most populous city (with a population of 9 million) in northwestern China, is located. Month-long (August 2011) WRF-Chem simulations with different sensitivity experiments were conducted and compared with near-surface measurements. Biogenic volatile organic compounds (VOCs) concentrations was characterized from six surface sites among the Qinling Mountains, and urban air composition was measured in Xi'an city at a tower 100 ma.s. The WRF-Chem control experiment reasonably reproduced the magnitudes and variations of observed O3, VOCs, NOx, PM2.5, and meteorological parameters, with normalized mean biases for each parameter within ±21 %. Subsequent analysis employed the factor separation approach (FSA) to quantitatively disentangle the pure and synergistic impacts of anthropogenic and/or biogenic sources on summertime O3 formation. The impact of anthropogenic sources alone was found to be dominant for O3 formation. Although anthropogenic particles reduced NO2 photolysis by up to 60 %, the anthropogenic sources contributed 19.1 ppb O3 formation on average for urban Xi'an. The abundant biogenic VOCs from the nearby forests promoted O3 formation in urban areas by interacting with the anthropogenic NOx. The calculated synergistic contribution (from both biogenic and anthropogenic sources) was up to 14.4 ppb in urban Xi'an, peaking in the afternoon. Our study reveals that the synergistic impact of individual source contributions to O3 formation should be considered in the formation of air pollution control strategies, especially for big cities in the vicinity of forests.

Ozone pollution over China and India: seasonality and sources

“…The estimated contribution of sources outside China declines to 46 % in summer, which agrees well with the 47 % value inferred from Nagashima et al (2010). Li et al (2012) applied the OSAT tool in the CAMx to apportion O 3 sources in South China, and they reported that superregional sources contributed 55 % and 71 % of monthly mean O 3 in summer and autumn, respectively. They also pointed out that regional and local sources play more important roles in O 3 pollution episodes (Li et al, 2002).…”

“…Strong but distinctive seasonal variations in O 3 observed in India and China have been linked to higher emissions of precursor gases (Lal et al, 2000) and summer monsoons (Kumar et al, 2010;Lu et al, 2018b;Wang et al, 2017). The contributions of individual economic sectors and source regions were reported based on sensitivity simulations and source apportionment techniques (Gao et al, 2016a;Li et al, , 2016Li et al, , 2012Lu et al, 2019;Wang et al, 2019). With respect to the enhanced concentrations of O 3 over the past years, Sun et al (2019) attributed them to elevated emissions of anthropogenic volatile organic compounds (VOCs), while Li et al (2019) argued that an inhibited aerosol sink for hydroperoxyl radicals induced by decreased PM 2.5 over 2013-2017 played a more important role in the North China Plain (NCP).…”

Land cover change dominates decadal trends of biogenic volatile organic compound (BVOC) emission in China

“…NOx/VOC emission would correspondingly promote the formation of ozone (Tang et al, 2010;Li et al, 2018;Li et al, 2019). Both AVOC and BVOC show the increasing trend since 2010, as shown in Figure 6, with an increase of 9.7% for AVOC and 34.6% for BVOC from 2010 to 2016, respectively.…”

“…The estimated increase of BVOC in regions like the Qinling Mountains and southern China are expected to affect regional air quality. For the Qinling Mountains and surrounding areas, as estimated by Li et al (2018) using the WRF-chem model, the average contribution of BVOC to O3 could reach 16.8 ppb for the https://doi.org /10.5194/acp-2020-28 Preprint. Discussion started: 16 March 2020 c Author(s) 2020.…”

“…Since BVOC plays an important role in local air 5 quality, the change of BVOC emission may have an even greater effect on the local ozone pollution. For instance, the simulation study by Li et al (2018) also found that the urban region of Xi'an is VOC-limited because of the abundant NOx emission there. Therefore, the increase of BVOC emission in the Qinling Mountains would further favor the formation of O3 in the urban region of Xi'an.…”