Aerosol optical properties in the North China Plain during HaChi campaign: an in-situ optical closure study

Abstract

The largest uncertainty in the estimation of radiative forcings on climate stems from atmospheric aerosols. In winter and summer of 2009, two periods of in-situ measurements on aerosol physical and chemical properties were conducted within the HaChi project at Wuqing, a town between Beijing and Tianjin in the North China Plain (NCP). Aerosol optical properties including scattering coefficient (σ<sub>sp</sub>), hemispheric back scattering coefficient (σ<sub>bsp</sub>), absorption coefficient (σ<sub>ap</sub>, as well as single scattering albedo (ω) are presented. The characteristics of diurnal and seasonal variations are analyzed together with the meteorological and satellite data. The mean values of σ<sub>sp, 550 nm</sub> of the dry aerosol in winter and summer are 280 ± 253 and 379 ± 251 Mm<sup>−1</sup>, respectively. The average σ<sub>ap</sub> for the two periods are respectively 47 ± 38 and 43 ± 27 Mm<sup>−1</sup>. The mean values of ω are 0.83 ± 0.05 and 0.87 ± 0.05 for winter and summer, respectively. The relative high levels of σ<sub>sp</sub> and σ<sub>bsp</sub> are representative of the regional polluted aerosol of the North China Plain. Pronounced diurnal cycle of σ<sub>sp</sub>, σ<sub>ap</sub> and ω are found, mainly influenced by the evolution of boundary layer and accumulation of local emissions during night-time. Regional transport of pollutants from southwest in the NCP is significant both in winter and summer, while high values of σ<sub>sp</sub> and σ<sub>ap</sub> correlate with calm winds in winter, which indicating the significant contribution of local emissions. An optical closure experiment is conducted to better understand uncertainties of the measurements. Good correlations (<i>R</i>>0.98) are found between values measured by nephelometer and values calculated with a modified Mie model. Monte Carlo simulations show an uncertainty of about 30% for the calculations. Considering all possible uncertainties of measurements, calculated σ<sub>sp</sub> and σ<sub>bsp</sub> agree well with measured values, indicating a stable performance of instruments and thus a reliable aerosol optical data

Seasonal variation and difference of aerosol optical properties in columnar and surface atmospheres over Shanghai

“…The Sc of Shanghai is lower than that of Guangzhou , Beijing (Jing et al, 2015) and their surrounding areas such as Xinken (Cheng et al, 2008b), Yufa (Garland et al, 2009) and Wuqing (Ma et al, 2011), and comparable to Delhi of India (Soni et al, 2010). In spite of different wavelengths, the Ab of Shanghai is far lower than that of Beijing (Jing et al, 2015), Guangzhou and their surrounding areas (Cheng et al, 2008b;Garland et al, 2009;Ma et al, 2011), andPasadena (Thompson et al, 2012) and Delhi (Soni et al, 2010). However, except rural sites in remote pristine areas or mountains (e.g.…”

A new method to determine the mixing state of light absorbing carbonaceous using the measured aerosol optical properties and number size distributions

“…1a 1.59 µg m −3 and a 95th percentage value of 15.87 µg m −3 . Futher details on aerosol optical properties for the HaChi summer campaign can be found in Ma et al (2011).…”

“…The raw TDMPS and APS data were inverted and merged to yield the PNSDs with the range of equivalent diameter from 3 nm to 10 µm. Details can be found in Ma et al (2011). The temporal resolution of the PNSD data was 10 min.…”

“…Three conceptual models are usually used to describe the mixing state of LAC and other aerosol components: external mixture, homogeneously internal mixture, and core-shell internal mixture (a LAC core surrounded by a well-mixed less absorbing shell) (Seinfeld and Pandis, 1998;Jacobson, 2001). Most of the models for estimating the direct aerosol radiative forcing, as well as aerosol optical closure studies (Wex et al, 2002b;Mallet et al, 2004;Cheng et al, 2006;Ma et al, 2011) are based on the assumption of external mixture or homogeneously internal mixture for LAC and less absorbing components. However, many studies have suggested that internally mixed LAC is usually coated with a shell of less absorbing component to form a core-shell structure rather than "well mixed".…”

Numerical simulation of diurnally varying thermal environment in a street canyon under haze-fog conditions

“…Based on field measurements data reviewed from literature (Ganguly et al, 2006;Zhao et al, 2013;Tao et al, 2014;Gao et al, 2015), four K ex values 0, 7e À4 , 1.71e À3 and 2.51e À3 /m are selected to represent four different levels of haze-fog weather conditions, from clear to heavily polluted weather. The single-scattering albedo (the ratio of scattering to extinction coefficient) is set as 0.9 based on previous studies (Ma et al, 2011;Zhao et al, 2013;.…”