Temporal variations of black carbon during haze and non-haze days in Beijing.

Qingyang Liu,Michael R Olson,James J Schauer,Tingting Zhang,Tangming Ma,Yu Wu,Yanju Liu

doi:10.1038/srep33331

Abstract

Black carbon (BC) aerosol has been identified as one of key factors responsible for air quality in Beijing. BC emissions abatement could help slow regional climate change while providing benefits for public health. In order to quantify its variations and contribution to air pollution, we systematically studied real-time measurements of equivalent black carbon (eBC) in PM2.5 aerosols at an urban site in Beijing from 2010 to 2014. Equivalent black carbon (eBC) is used instead of black carbon (BC) for data derived from Aethalometer-31 measurement. Equivalent BC concentrations showed significant temporal variations with seasonal mean concentration varying between 2.13 and 5.97 μg m−3. The highest concentrations of eBC were found during autumn and winter, and the lowest concentrations occurred in spring. We assessed the temporal variations of eBC concentration during haze days versus non-haze days and found significantly lower eBC fractions in PM2.5 on haze days compared to those on non-haze days. Finally, we observed a clear inverse relationship between eBC and wind speed. Our results show that wind disperses PM2.5 more efficiently than eBC; so, secondary aerosols are not formed to the same degree as primary aerosols over the same transport distance during windy conditions.

Highlights

Black carbon (BC) aerosol is formed by the incomplete combustion of fuels and is an important atmospheric components because of its potentially negative effects on climate and health[1,2,3]
Substantial efforts have been made by the Beijing government to reduce air pollution since the 1990s, the focus has largely been on reductions of emissions from fossil and solid fuel combustion, while the contribution from secondary aerosols has been relatively neglected due to the lack of relevant long-term scientific data to explain its role in air pollution
We found significantly lower equivalent BC fractions in PM2.5 on haze days compared to those on non-haze days from 2010 to 2014, which directly confirms that primary aerosols (i.e. BC) have a relatively smaller contribution to haze formation and proves that secondary aerosols have a significantly greater contribution to Beijing air pollution

Summary

Introduction

Black carbon (BC) aerosol is formed by the incomplete combustion of fuels and is an important atmospheric components because of its potentially negative effects on climate and health[1,2,3]. China is the largest emitter of BC in Asia, and the predominant sources include residential combustion (55.3%), industrial emissions (31.8%), transportation (10.9%) and power production (1.8%)[14].The transportation sector has been recognized as a significant contributor to BC emissions in the urban atmosphere of China[18]. For 5 years, equivalent BC was continuously measured at a roadside site in urban Beijing and analyzed for daily, seasonal, and annual variations in order to identify how they relate to source emissions and meteorology. This study contributes to field of emission abatement by providing new information regarding measurement of equivalent BC concentrations and identification of sources It is complemented by parallel studies concerning optimization of air quality regulations for developing countries, such as China

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Results

Conclusion