Measurements of traffic-dominated pollutant emissions in a Chinese megacity

Freya Squires ,W Joe F Acton,Ruili Wu,C Nicholas Hewitt,Qiang Zhang,Pingqing Fu,James Lee,Oliver Wild,Xinming Wang,Stefan Metzger,Simone Kotthaus,Will S Drysdale,Marvin Shaw,Eiko Nemitz,Jacqueline F Hamilton,Michael Hollaway,Yanli Zhang,B Langford ,Adam Vaughan ,Sue Grimmond ,Natchaya Pingintha‐Durden

doi:10.5194/acp-20-8737-2020

Abstract

Abstract. Direct measurements of NOx, CO and aromatic volatile organic compound (VOC) (benzene, toluene, C2-benzenes and C3-benzenes) flux were made for a central area of Beijing using the eddy-covariance technique. Measurements were made during two intensive field campaigns in central Beijing as part of the Air Pollution and Human Health (APHH) project, the first in November–December 2016 and the second during May–June 2017, to contrast wintertime and summertime emission rates. There was little difference in the magnitude of NOx flux between the two seasons (mean NOx flux was 4.41 mg m−2 h−1 in the winter compared to 3.55 mg m−2 h−1 in the summer). CO showed greater seasonal variation, with mean CO flux in the winter campaign (34.7 mg m−2 h−1) being over twice that of the summer campaign (15.2 mg m−2 h−1). Larger emissions of aromatic VOCs in summer were attributed to increased evaporation due to higher temperatures. The largest fluxes in NOx and CO generally occurred during the morning and evening rush hour periods, indicating a major traffic source with high midday emissions of CO, indicating an additional influence from cooking fuel. Measured NOx and CO fluxes were then compared to the MEIC 2013 emissions inventory, which was found to significantly overestimate emissions for this region, providing evidence that proxy-based emissions inventories have positive biases in urban centres. This first set of pollutant fluxes measured in Beijing provides an important benchmark of emissions from the city which can help to inform and evaluate current emissions inventories.

Highlights

Rapid development and population growth have led to an ever increasing number of “megacities”, defined by the United Nations (UN) as a “metropolitan area with a total population of more than 10 million people” (United Nations Department of Economic and Social Affairs, Population Division, 2016)
Concentrations of ozone, O3, a major component of photochemical smog, regularly exceeded the World Health Organisation (WHO) 8 h mean limit of 100 μg m−3 in Beijing. Both particulate matter (PM) and O3 have detrimental impacts on public health and both are formed in the atmosphere from reactions by precursor emissions that include nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs)
For CO, there was a larger difference between the two seasons, with the mean flux calculated as 35 ± 40 mg m−2 h−1 for winter and 15 ± 14 mg m−2 h−1 in summer

Summary

Introduction

In addition to being home to a large population, megacities are typically associated with high levels of industrialisation and extensive transportation networks, making air pollution a common problem. Beijing is one such city that regularly experiences significant air quality problems. Liu et al (2018) concluded that there is an association between shortterm exposure to ambient CO and increased cardiovascular disease mortality, especially coronary heart disease mortality For both these pollutants, traffic emissions tend to be the dominant source in megacities

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Conclusion