Abstract

Abstract. With the increase in economic development over the past thirty years, many large cities in eastern and southwestern China are experiencing increased haze events and atmospheric pollution, causing significant impacts on the regional environment and even climate. However, knowledge on the aerosol physical and chemical properties in heavy haze conditions is still insufficient. In this study, two winter heavy haze events in Beijing that occurred in 2011 and 2012 were selected and investigated by using the ground-based remote sensing measurements. We used a CIMEL CE318 sun–sky radiometer to retrieve haze aerosol optical, physical and chemical properties, including aerosol optical depth (AOD), size distribution, complex refractive indices and aerosol fractions identified as black carbon (BC), brown carbon (BrC), mineral dust (DU), ammonium sulfate-like (AS) components and aerosol water content (AW). The retrieval results from a total of five haze days showed that the aerosol loading and properties during the two winter haze events were comparable. Therefore, average heavy haze property parameters were drawn to present a research case for future studies. The average AOD is about 3.0 at 440 nm, and the Ångström exponent is 1.3 from 440 to 870 nm. The fine-mode AOD is 2.8 corresponding to a fine-mode fraction of 0.93. The coarse particles occupied a considerable volume fraction of the bimodal size distribution in winter haze events, with the mean particle radius of 0.21 and 2.9 μm for the fine and coarse modes respectively. The real part of the refractive indices exhibited a relatively flat spectral behavior with an average value of 1.48 from 440 to 1020 nm. The imaginary part showed spectral variation, with the value at 440 nm (about 0.013) higher than the other three wavelengths (about 0.008 at 675 nm). The aerosol composition retrieval results showed that volume fractions of BC, BrC, DU, AS and AW are 1, 2, 49, 15 and 33%, respectively, on average for the investigated haze events. The preliminary uncertainty estimation and comparison of these remote sensing results with in situ BC and PM2.5 measurements are also presented in the paper.

Highlights

  • Haze can reduce severely atmospheric visibility due to increased extinction of suspended solid or liquid particles

  • The black carbon (BC) mass concentration obtained from AE51 during this period is plotted in Fig. 12, which corresponds to BC content of the surface layer

  • We proposed a rough selection criterion of aerosol optical depth (AOD)(440 nm) > 1.0, α > 1.0 and relative humidity (RH) < 90 % to select heavy haze condition, based on the ground-based sun–sky radiometer measurements

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Summary

Introduction

Haze can reduce severely atmospheric visibility due to increased extinction of suspended solid or liquid particles. One major constituent of haze is aerosol particles, such as dust and soot from fuel- or coal burning. Environmental air is usually polluted, and affects human health. It has significant effects on cloud formation and regional climate. Haze event has been observed frequently in Beijing (Sun et al, 2006), during the cold winter and spring seasons because of the enhanced heating, traffic and industrial emissions, and especially the stable weather conditions. Studies on the haze pollution in Beijing are rather limited, and simultaneous observation of physical and optical properties as well as the chemical characteristics of haze aerosol even less so

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