Assessment of column aerosol optical properties using ground-based sun-photometer at urban Harbin, Northeast China

Aerosol plays a key role in determining radiative balance, regional climate and human health.Severe air pollution over Northeast China in recent years urges more comprehensive studies to figure out the adverse effects caused by excessive aerosols. In this study, column aerosol measurements over urban Harbin, a metropolis located at the highest latitude in Northeast China, during May 2016 to March 2017 were conducted using a CIMEL sun-photometer to analyze local aerosol properties and its variation from different aspects. According to the observations, aerosol optical depth at 440 nm（AOD_（440）） ranges from 0.07 up to 1.54, and the large variability in both AOD_（440） and Angstrom Exponent（AE_（440–870）） indicates the frequent change of aerosol types due of different emission sources. Coarse mode particles dominated Harbin during the studying period because of the long-range transported dust and probably the suspended snow crystals in winter. As the wavelength increases, relatively consistent decrease trends of single scattering albedo（SSA） and asymmetry factor（ASY） were observed in spring, autumn, and winter, indicating the presence of absorbing polluted aerosols. Mixed type（MIX） aerosol dominated the study region with a total percentage of 34%, and biomass burning and urban industry（BB/UI）, clean continental（CC）, and desert dust（DD） aerosols were found to be 31%, 27%, and 8%, respectively. The current work fills up the optical characteristics of aerosols in Harbin, and will contribute to the in-depth understanding of local aerosol variation and regional climate change over Northeast China.

Aerosol properties over an urban site in central East China derived from ground sun-photometer measurements

Sun-photometer measurements at Hefei,an urban site located in central East China,were examined to investigate the variations of aerosol loading and optical properties.It is found that aerosol optical thickness(AOT)keeps higher in winter/spring and gets relatively lower in summer/autumn.The large AOT in winter is caused by anthropogenic sulfate/nitrate aerosols,while in spring dust particles elevate the background aerosol loading and the excessive fine-mode particles eventually lead to severe pollution.There is a dramatic decline of AOT during summer,with monthly averaged AOT reaching the maximum in June and soon the minimum in August.Meanwhile,aerosol size decreases consistently and single scattering albedo(SSA)reaches its minimum in July.During summertime large-sized particles play a key role to change the air from clean to mild-pollution situation,while the presence of massive small-sized particles makes the air being even more polluted.These complicated summer patterns are possibly related to the three key processes that are active in the high temperature/humidity environment concentrating on sulfate/nitrate aerosols,i.e.,gas-to-particle transformation,hygroscopic growth,and wet scavenging.Regardless of season,the increase of SSA with increasing AOT occurs across the visible and near-infrared bands,suggesting the dominant negative/cooling effect with the elevated aerosol loading.The SSA spectra under varying AOT monotonically decrease with wavelength.The relatively large slope arises in summer,reinforcing the dominance of sulfate/nitrate aerosols that induce severe pollution in summer season around this city.

Analysis of the Aerosol Extinction Characteristics in Different Areas of China

The multi-wavelength aerosol optical depths and the Angstrom exponent between 450 nm and 900 nm in four locations of China (Miyun, Beijing; Xinfeng, Guangdong; Waliguan, Qinghai and Damxung, Tibet) have been observed by sun-photometers. This paper analyzes their characteristics for a one-year period from February 1998 to January 1999. The results show that in the arid and semi-arid locations like Miyun (117.12°E, 40.65°N) and Waliguan (100.90°E, 36.29°N), there is a maximum of aerosol optical depth in the spring, it is about twice as large as in any other season. In a humid region like Xinfeng (114.2“E, 24.5°N), the aerosol optical depth also has a maximum in the spring, however it is only slightly larger than in other seasons. The Angstrom exponent shows a significant minimum at Waliguan in spring, about 0.15, indicating relatively large dust aerosol particles. Large variability of the monthly mean Angstrom exponent is also found in Miyun and Xinfeng, but there is no tendency with seasons. It means that the source of aerosol in these locations is complicated.