Introduction to Special Issue – In-depth study of air pollution sources and processes within Beijing and its surrounding region (APHH-Beijing)

Abstract

<p><strong>Abstract.</strong> APHH-Beijing (Atmospheric Pollution and Human Health in a Chinese Megacity) is an international collaborative project to examine the emissions, processes and health effects of air pollution in Beijing. The four research themes of APHH-China are: (1) sources and emissions of urban atmospheric pollution; (2) processes affecting urban atmospheric pollution; (3) exposure science and impacts on health; and (4) interventions and solutions to reduce health impacts. Themes 1 and 2 are closely integrated and support Theme 3, while Themes 1–3 provide scientific data for Theme 4 on the development of cost-effective solutions. A key activity within APHH-Beijing was the two month-long intensive field campaigns at two sites: (i) central Beijing, and (ii) rural Pinggu. The coordinated campaigns provided observations of the atmospheric chemistry and physics in and around Beijing during November–December 2016 and May–June 2017. The campaigns were complemented by numerical air quality modelling and air quality and meteorology data at the 12 national monitoring stations in Beijing. This introduction paper provides an overview of (i) APHH-Beijing programme, (ii) the measurement and modelling activities performed as part of it in Beijing, and (iii) the air quality and meteorological conditions during the two field campaigns. The winter campaign was characterized by high PM<sub>2.5</sub> pollution events whereas the summer experienced high ozone pollution events. Air quality was poor during the winter campaign, but less severe than in the same period in 2015 when there were a number of major pollution episodes. PM<sub>2.5</sub> levels were relatively low during the summer period, matching the cleanest periods over the previous five years. Synoptic scale meteorological analysis suggests that the greater stagnation and weak southerly circulation in November/December 2016 may have contributed to the poor air quality.</p>

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: roles of regional transport and heterogeneous reactions of SO<sub>2</sub>

“…2.1. The regional transport defined by Sun et al (2014) was LTC + RLC + RTC, whereas in the studies by J. and Timmermans et al (2017), it was RLC + RTC. In this study, we employed RLC + RTC as regional transport.…”

“…These formed sulfates may have been blown back to Beijing under specific weather conditions and were previously considered regional transport. The contribution of LTC also largely explains the difference in estimated regional transport contributions between Sun et al (2014) and J. . In the present study, LTC + RLC + RTC accounted for 58 %-70 % of the sulfate concentration in the six episodes, which is relatively similar to the estimation (75 %) of Sun et al (2014), which was based on the observed hourly increase rate of the local sulfate concentration.…”

“…Quantifying the impact of regional transport of sulfate and its precursors is a crucial task. Sun et al (2014) considered sulfate formed outside Beijing as regionally transported sulfate, and they estimated that its contribution reached 75 % during winter haze episodes. By tagging emission regions of precursors in models and ignoring where secondary aerosols were formed, J. and Timmermans et al (2017) estimated the contribution of transport to be 40 %-50 %.…”

“…In past decades, a megacity cluster in China that is centered on Beijing and includes 28 cities (272 500 km 2 , with a population of 191.7 million people) has experienced frequent severe and persistent haze episodes (Zhao et al, 2013;Sun et al, 2014Sun et al, , 2016. PM 2.5 levels exceeding 500 µg m −3 have often been reported.…”

Measurements of traffic dominated pollutant emissions in a Chinese megacity

“…To the knowledge of the authors, this is the first time these emissions have been directly quantified in Beijing. This work was carried out as part of the Air Pollution and Human Health (APHH) Beijing project and an overview of this campaign can be found in Shi et al (2019). Instrumentation was housed in a temporary shipping container laboratory located at the base of the tower.…”