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

Nan Li,Qiang Zhang,Qiyuan Wang,Jim Greenberg,Junji Cao,Alex Guenther,Jingyi Li,Qingyang He,Jun Wang,Hong Liao

doi:10.5194/acp-18-7489-2018

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.

Highlights

Elevated ozone (O3) levels in China have drawn increasing attention in recent years (e.g., Xue et al, 2014; Hu et al, 2016; Wang et al, 2017, 2016)
We addressed that the uncertainties of volatile organic compounds (VOCs) emission obviously affected the VOC concentrations; MEIC inventory is the most updated available emission for China so far, and quantifying its uncertainties can be done in future studies
The GZ Basin is a representative region in the northwest of China, suffering serious air pollution in recent years

Summary

Introduction

Elevated ozone (O3) levels in China have drawn increasing attention in recent years (e.g., Xue et al, 2014; Hu et al, 2016; Wang et al, 2017, 2016). The surface O3 level has been increasing in most Chinese cities. In the highly urbanized areas of China, maximum 8 h O3 concentration increased by 19 % (16.9 ppb) from 2015 to 2017 in the Beijing–Tianjin–Hebei (BTH) region, the growth trend was 14 % (11.3 ppb) for the Pearl River delta (PRD) region and 12 % (10.5 ppb) for the Yangtze River delta (YRD) region (http://106.37.208.233:20035/, last access: 29 May 2018). The pollution trend is likely to worsen due to potential changes of climate and emissions (Wang et al, 2013; Liu et al, 2013; Zhu et al, 2016, 2017)

Objectives

Methods

Findings

Conclusion