An intensive study of aerosol optical properties in Beijing urban area

Abstract

Abstract. In order to quantify the aerosol impact on climate, a range of aerosol parameters are required. In this paper, twoyear of ground-based observations of aerosol optical properties from an urban site in Beijing of China are assessed. The aerosol absorption coefficient (σ a ), scattering coefficient (σ s ), as well as single scattering albedo (ω) are analyzed to aid in characterizing Beijing's urban aerosol. Two-year averages (and standard deviations) for σ a at 532 nm, σ s at 525 nm and ω at 525 nm are 56±49 Mm −1 , 288±281 Mm −1 and 0.80±0.09, respectively. Meanwhile, there is a distinct diurnal variation for σ a , with its minimum occurring at approximately 14:00 to 15:00 and maximum at midnight. σ s peaks in the late morning and the minimum occurs in the evening. σ s in summer is higher than that in winter. ω is also higher in summer than that in winter, except before 07:00 a.m., and peaks in the early afternoon. Both σ a and σ s show strong dependence on local wind in all four seasons. When the wind blows from the north with low speed (0-2 m/s), the values of σ a are high, and in contrast, very low with wind speeds higher than 4 m/s. When the wind blows from south with low speed (0-4 m/s), σ a is intermediate. The patterns of the wind dependence of σ a indicates that σ a is mainly dominated by local emissions. σ s displays a similar dependence on wind speed and direction to σ a , except in summer. In summer, the σ s value is highest when wind is from southeast with speed of 0-6 m/s. This indicates that the particle pollution resulting from regional transport is only significant in the summer season. ω also shows wind dependence to some extent though not as strong as σ a or σ s . Overall, the wind dependence results provide valuable information about the locations of Correspondence to: C. C. Li (ccli@pku.edu.cn) aerosol pollution sources and suggest that the air pollution in summer is a regional problem but in other seasons it is mainly affected by local urban emissions.

AERONET-based models of smoke-dominated aerosol near source regions and transported over oceans, and implications for satellite retrievals of aerosol optical depth

“…Eck et al, 1999;Dubovik et al, 2002;Salinas et al, 2009;Bovchaliuk et al, 2013) or other techniques (e.g. He et al, 2009;Gyawali et al, 2012;McMeeking et al, 2012). On the one hand this means that optical models based on smoke may also be appropriate optical proxies for mixed smoke/urban or urban aerosols in some cases (although again commonality of optical properties should not be taken to imply commonality of microphysical properties or origin).…”

Variability of aerosol optical properties in the Western Mediterranean Basin

“…An average value of σ (λ) = 10.4±2.0 m 2 g −1 was obtained and used to calculate the EBC presented in this work. Absorption cross sections between 7 m 2 g −1 and 11 m 2 g −1 are usually reported in literature (see for example Bond and Bergstrom, 2006;Fernández-Camacho et al, 2010;He et al, 2009;Barnard et al, 2008;Arnott et al, 2003Arnott et al, , 2005Reche et al, 2011)). …”

“…During the measurement period the scattering and hemispheric backscattering coefficients (@ 635 nm) ranged between 0. (He et al, 2009) and Mexico City (Silvia, 2002;Paredes-Miranda et al, 2009). Scattering and absorption coefficients with mean values higher than 700 Mm −1 and 80 Mm −1 respectively were measured in a highly polluted site close to New Delhi (Hyvärinen et al, 2010).…”

Absorption coefficient of urban aerosol in Nanjing, west Yangtze River Delta, China

“…The AAC at 565 nm in the Gobi Desert was found to be as low as 6 ± 11 M m −1 (Yulin) (Xu et al, 2004). The annual 532 nm AAC was about 17.54 ± 13.44 M m −1 at a rural site, while it was about 45 ± 39 M m −1 at an urban site, in Beijing (Yan et al, 2008;He et al, 2009). The AAC at 532 nm was as large as 82 ± 23 M m −1 in the urban area of Pearl River Delta (PRD) in south China (Wu et al, 2009).…”

“…The BC aerosols are mostly emitted in southwest and north China, in the regions of Yangtze River Delta (YRD) and Pearl River Delta (PRD) . Recently, many observation-based studies have been conducted on the aerosol optical properties and direct radiative forcing over China (Xu et al, 2004;Yan, 2006;Xia et al, 2007;Yan et al, 2008;He et al, 2009;Wang et al, 2009;Wu et al, 2009;Li et al, 2010;Cai et al, 2011;Bai et al, 2011;Xiao et al, 2011;Zhou et al, 2011;Wu et al, 2012;etc.). Some of them focused on the total extinction or optical depth of the aerosols.…”