Meteorological dependence of particle number concentrations in an urban area of complex terrain, Northwestern China
2015
Zhao, Suping | Yu, Ye | Yin, Daiying | He, Jianjun
To understand the effects of meteorological conditions on particle number concentrations and their size distributions in a typical valley city, measurements for particles in the size range 10 to 10,000nm were conducted using TSI particle sizer (SMPS-3936 and APS-3321) from 1 September 2012 to 31 August 2013 in urban Lanzhou. The particle number concentrations in large nucleation (10–25nm), Aitken (25–100nm) and accumulation modes (100–1000nm) depended on different meteorological parameters in four seasons. The relationships between number concentrations of large nucleation mode particles and meteorological conditions were unobvious for non-NPF (New Particle Formation) event. The number concentrations of particles in Aitken and accumulation modes mainly relied on wind speed in spring and winter, while those depended not only on wind speed but also on temperature in summer and fall. Additionally, particle number concentrations in accumulation mode increased as increase of RH in summer due to hygroscopic growth of smaller particles. There was a burst of particle number concentration in the large nucleation mode followed by subsequent particle growth for NPF events, and the events were discerned easily when temperature and wind speed were higher than 20°C and 2.0ms−1 in spring and summer. The mode diameters of particle number size distributions significantly decreased as temperature increased in summer and fall, while those decreased from ~70nm to ~20nm with increases of wind speed in four seasons in urban Lanzhou.
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