Waliguan Region Aerosol Number Spectra Observation And Research

Ambient particles are ubiquitous,influencing the global climate and causing adverse effects.Particle number size distributions are basis to understand the particle behavior and transformation as well as these effects in the atmosphere.From August 2005 to May 2007,particle number size distributions between 10nm and 500nm have been taken measurements for 22 months in Mt.Waliguan.During this period,the average particle number concentration are:total 2102cm^-3;Nucleation mode 456cm^-3; Aitken mode 1161cm^-3;Accumulation mode 474cm^-3.Particle number concentration is about one magnitude lower than that in urban area.Particle number concentration and particle number size distributions have seasonal variation.The highest particle number concentration was observed in summer,and the lowest in autumn.The particle number concentrations are dominated by Aitken mode.In winter nucleation mode particle concentration is higher than other season because of lower ambient temperature and relative humidity.For the transportation,Aitken mode particle concentration is highest in summer,which may results from the transportation.The average number concentration in autumn is the lowest as there are more foggy days in autumn.Meteorological factors strongly affect the particle number size distributions.Dust storm and precipitations strongly affect the Aitken and accumulation mode particle number concentration,but they have little influence on nucleation mode.If the wind blow from northeast,number concentration of Aiken mode will increase.If the wind blow from northwest or north,number concentration of nucleation mode will increase.Cluster analysis of backward trajectories shows that the higher Aitken mode particle number concentration observed when air parcels come from or pass by northeast of Mt.Waliguan,with short trajectory length.High number concentrations of nucleation mode are associated with air mass from clean regions,with long trajectory length.New particle formation and growth events were also observed in Mt.Waliguan.The frequency of new particle formation events were observed around 23%of measure days.The events occurred during all seasons,but with highest frequency in winter and lowest in summer. The formation rates varied from 2.27～5.29 cm^-3s^-1..The growth rate varied from 0.05～4.07 nm h^-1.The growth rate in summer is higher than other seasons.It could be related to high condensable vapor transported from northeast and/or from enhanced photochemical product. Because of lower temperature and relative humidity,the formation rate in winter and spring are higher.