Characteristics Of Atmospheric Particle Number Concentration And Size Distribution In Urban Jinan

Atmospheric particles are the most common and most important air pollutants in China, which have impact not only human health, but also on visibility, formation of acid rain, cloud formation, and ecosystem. At present, in the growing concern of global climate change, atmospheric particles are being paid more and more attentions, because of their impact on radioactive forcing. Number concentration and size distribution are important parameters of atmospheric particles and emphasis of research on particles. Research on nucleation and growth of particles is a new field of research based on particle number concentration and size distribution.In order to research characteristics of particle number concentration, size distribution, new particle formation, and particle growth in urban areas suffering serious atmospheric pollution, measurements in urban Jinan was operated for about 6 months from December 2007 to October 2008, and atmospheric particle number concentrations and size distributions, SO2, NOx, O3, mass concentrations and water-soluble ions of PM2.5, and meteorological parameters were measured. Particle (10 nm-10μm) number concentrations and distributions of urban Jinan achieved by advanced instrument (Wide -range Particle Spectrometer, WPS) and diurnal characteristics of these data were analyzed. Differences of particle number concentrations and size distributions between weekdays and weekends, between hazy days and non-hazy days were studies. New particle formation and particle growth in urban Jinan was analyzed for learning characteristics of that of cities in north China.Main results are followed:1. The annual number concentration of urban Jinan is 15734 cm-3,and that of winter is the highest and that of fall is the lowest. The number concentration is dominated by accumulation mode (50-2000 nm) and Aitken mode (20-50 nm). Similar to number concentrations, the surface and volume are also dominated by accumulation-mode particles. Compared with urban studies in Europe and US, Jinan has lower number concentrations of 10-100 nm, but higher concentrations of 100-500 nm. In summer, the size distribution of number concentration has a peak around 1μm, which is originate from agricultural biomass burning. In fall, hours with high number concentrations occurred more frequently than other seasons.Compared with urban studies in Europe and US, variations of particle number concentration and related gaseous pollutant concentrations in Jinan between weekdays and weekends are smaller and the reasons has been deduced from social practice characteristics and terrain, respectively. The role of particles (100-500 nm & 500-2000 nm) in haze formation is obvious, and conditions of haze are unfavorable to new particle formation and existence of nucleation-mode particles.2. Through analyses of the diurnal of number concentrations and size distributions of Jinan, it is concluded that number concentrations are obviously influenced by traffic emissions, especially during the morning and evening rush hours, and other hours with weaker dispersion capacity At midday, the number concentrations are greatly influenced by air mass transported from suburban and rural areas. Diurnals of size distribution show obvious seasonal characteristics:more new particle formation events were observed in fall, not obvious peak during morning and evening rush hours for summer and serious pollution for winter. In summer, mass concentrations of PM2.5 are the highest perhaps originated from formation of droplet mode and biomass burning. Most common styles of diurnal of size distribution have been classified into 4 types:more type IV in fall, and more type I and III in winter.3. Jinan has lower frequencies of new particle formation events compared with other urban researches. In fall, the frequencies of new particle formation events are the highest and other seasons have very few events. Parameters of nucleation and growth were calculated through binary nucleation theory. New particle formation rates (J10) varied from 1.1 to 2.4 cm-3·s-1, averaged 1.8 cm-3·s-1; growth rates of diameter (GR) varied from 1.7-11.7 nm·h-1, averaged 4.7 nm·h-1; condensation sinks (CS) varied from 0.63×10-2 to 6.6×10-2 s-1, averaged 2.3×10-2 s-1; the condensable vapor concentrations (C) varied from 2.5×107 to 14×107 cm-3, averaged 5.5×107 cm-3 source rates of condensable vapor varied from 0.25×106 to 6.4×106 cm-3·s-1,averaged 1.8×106 cm-3·s-1. Most of these parameters were similar with those of Beijing and higher than those of European cities.4. The number concentration of nucleation mode in Jinan is decreased by higher CS and CoagS (coagulation sink) through restricting formation of new particles, existences of condensable vapor and nano-particles. CS and CoagS of fall were the lowest and those of winter were the highest, because CS and CoagS of Jinan are dominated by accumulation-mode particles. Diurnals of CS and CoagS indicate that CS and CoagS are influenced by traffic emissions and air mass transported from suburban and rural areas.5. It could be deduced that regional nucleation events occur frequently around Jinan and the North China Plain from frequent particle growth events observed in Jinan. It could be also deduced that new particle formation is an important source of PM2.5 in this area, and an important source of Aitken mode and accumulation mode particles, CS, and CoagS of urban Jinan.