Effects of air mass sources and fog event on the number spectrum distribution of submicron aerosols over the alpine background area in South China
To improve our understanding of the physical and chemical characteristics of aerosols in the background atmosphere in South China,the Scanning Mobility Particle Sizer(SMPS)were applied for the first time to measure the number concentration and particle number size distributions(PNSD)of submicron particulate matter(PM)at the Nanling National Atmospheric Background Station(Nanling site,1690m a.s.l.).Concurrently,the characteristics of PNSD under different sources of air mass and meteorological conditions along with variations in both the aerosol number concentration and the PNSD during a typical fog event were evaluated.Our results show that the average particle number concentration at the Nanling site was 1.14×103cm-3,being lower than most of the domestic and international mountainous background sites and exhibiting a relatively clean atmosphere;and the average particle number concentration was higher in the afternoon than in the morning with a peak concentration at around 2pm.During the observation period,the station was mainly influenced by the southern air masses(66.2％)originating from the South China Sea passing through the Pearl River Delta megacities,and the northern air masses(33.8％)passing through Hunan Province.The PNSD under the southern and northern air masses exhibited bimodal distributions,but the average aerosol number concentration from the southern air masses was twice that from the northern air masses(7.9× 102cm 3),and the number concentration of particles within a range of 40-300nm increased significantly.The number concentrations of aerosols in the Nuclear mode and Accumulation mode were 80％lower under the foggy weather than under non-foggy weather,showing an obvious aerosol scavenging effect of fog;During the development of a fog event,the PNSD evolved from bimodal to unimodal,then to bimodal,demonstrating that the spectral width narrowed and the peak value of aerosol number concentration shifted towards smaller particle sizes.In general,the aerosols were mainly present in Nuclear mode and Accumulation mode(the two account for more than 95％of the total concentration),and the low aerosol number concentration was mainly attributed to the frequent foggy weather at Nanling Station.
Nanling mountainsNational Atmospheric Background Stationfine particlessize distributionair mass transportfog
万方数据
维普
