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Abstract
Abstract. The largest uncertainty in the estimation of climate forcing stems from atmospheric aerosols. In early spring and summer of 2009, two periods of in-situ measurements on aerosol physical and chemical properties were conducted within the HaChi (Haze in China) project at Wuqing, a town between Beijing and Tianjin in the North China Plain (NCP). Aerosol optical properties, including the scattering coefficient (σsp), the hemispheric back scattering coefficient (σbsp), the absorption coefficient (σap), as well as the single scattering albedo (ω), are presented. The diurnal and seasonal variations are analyzed together with meteorology and satellite data. The mean values of σsp, 550 nm of the dry aerosol in spring and summer are 280±253 and 379±251 Mm−1, respectively. The average σap for the two periods is respectively 47±38 and 43±27 Mm−1. The mean values of ω at the wavelength of 637 nm are 0.82±0.05 and 0.86±0.05 for spring and summer, respectively. The relative high levels of σsp and σbsp are representative of the regional aerosol pollution in the NCP. Pronounced diurnal cycle of $σsp, σap and ω are found, mainly influenced by the evolution of boundary layer and the accumulation of local emissions during nighttime. The pollutants transported from the southwest of the NCP are more significant than that from the two megacities, Beijing and Tianjin, in both spring and summer. An optical closure experiment is conducted to better understand the uncertainties of the measurements. Good correlations (R>0.98) are found between the values measured by the nephelometer and the values calculated with a modified Mie model. The Monte Carlo simulation shows an uncertainty of about 30 % for the calculations. Considering all possible uncertainties of measurements, calculated σsp and σbsp agree well with the measured values, indicating a stable performance of instruments and thus reliable aerosol optical data.
Highlights
Atmospheric aerosols influence the earth’s radiation budget directly by scattering and absorbing solar radiation (Charlson et al, 1992), and indirectly by acting as condensation nuclei in cloud formation, affecting the optical properties and lifetimes of clouds (Twomey, 1974; Albrecht, 1989; Rosenfeld, 1999, 2000)
Ma et al.: Aerosol optical properties in the North China Plain during HaChi Campaign coefficient, absorption coefficient, aerosol optical depth (AOD) and single scattering albedo (ω), are closely related to the aerosol physical and chemical characteristics, which are influenced by many processes, such as aerosol formation, growth and removal
The calculations are based on measured particle number size distributions (PNSDs) and the black carbon (BC) concentrations
Summary
Atmospheric aerosols influence the earth’s radiation budget directly by scattering and absorbing solar radiation (Charlson et al, 1992), and indirectly by acting as condensation nuclei in cloud formation, affecting the optical properties and lifetimes of clouds (Twomey, 1974; Albrecht, 1989; Rosenfeld, 1999, 2000). N. Ma et al.: Aerosol optical properties in the North China Plain during HaChi Campaign. Due to the uncertainties in measurements and models, the calculations are needed to be evaluated (Quinn et al, 1998; Bond et al, 1998; Sheridan et al, 2001). Closure studies are usually used for estimating the uncertainties of measurement techniques and numerical models. There were some studies focusing on aerosol optical properties (Yan et al, 2008; Xu et al, 2002, 2004; Cheng, 2008a, 2009), but only a few studies touched the uncertainty evaluation of measured aerosol properties and related models (Cheng et al, 2007). An aerosol optical closure study between measured and calculated aerosol scattering coefficients and the related uncertainty evaluation are shown
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