Distribution Of Atmospheric Particle Number Concentration In Qingdao And Variations In Different Weather Conditions

Atmospheric particles could influence the characters of the atmosphere and the globalclimate. They also have great effects on human health. The aerosol mass and particlenumber concentrations are highly variable in space and time. A detailed knowledge ofchemical and physical properties of aerosols is needed to estimate and predict theecological and environmental effect of the particles. Size distribution of atmosphericparticles in number concentration could become relevant to perform these estimations.Therefore it is important to characterize the particles in different geographical areas. Forthis reason, in the last decade measurements of particle number concentrations and sizedistributions have been performed in different locations in the world. Qingdao is locatedin the south of Shandong peninsula, bordering the Yellow Sea, where is in the downwindregion of the Asia dust source area and North China urban agglomeration. Particles areimportant pollutants especially when the wind comes from the northwest of China inspringtime. So it’s all-important to explore the aerosol characteristics and the atmosphericdeposition. The particle number concentration and size distribution were measured inQingdao since March2010to July2011. The seasonal variations, air mass origins andmeteorological conditions were discussed in this paper, and compared with the data overthe sea which measured during the cruise campaigns in2011. The particles dry depositionvelocity and flux were also estimated.Particle (>0.3μm) number concentration in Qingdao is at range of2.7~541.6cm-3,261.8cm-3on average. With the particle size increasing, the number concentrationdecreases gradually.0.3~0.5μm,0.5~0.7μm particles are90%of the total, while0.7~1.0μm,1.0~2.0μm,2.0~5.0μm are about10%. The seasonal variations show that thenumber concentrations of the particles <1.0μm are low in spring. But>2.0μm particlesare maximum in spring and minimum in summer. In springtime the dust events have greatcontribution to the coarses. In summer the aerosols are influenced by the maritime airmass. In autumn and winter they are affected by the north land sources. The particlenumber concentrations and size distributions are also likely related to air mass trajectories.Number concentrations of the fine particle are much higher when the air mass comingfrom the south. The coarses are highest when they originated from the desert.Weather conditions could also impact the size distribution of atmospheric particles in number concentration significantly. Before the dust events number concentrations ofparticles at0.3~1.0μm size range increase a little, then reduce by20%~45%during dustevents. However, number concentrations of particles>1.0μm increase a lot during thedust events. The increase is obvious for0.5~1.0μm particles during haze events and thenumber concentrations of particles <1.0μm keep the maximum. Rainfall clear awayparticles especially the coarses(>1.0μm). After the rain fine particles reappear quickly.From the data observed during the cruise campaigns2011, we find that the particlenumber concentration in May to June over the East China Sea varies from0.1to71.7cm-3(mean14.4cm-3), while in October over the East China Sea and Yellow Sea is from3.2to48.5cm-3(mean12.2cm-3), much lower than that measured at the same period inQingdao. The number concentrations of particles at0.3~0.5μm size range in Qingdao isthe highest. But over the China Sea, the particle number-size distribution is characterizedby a multimodal distribution, where the peaks appear both in fine mode (0.5~1.0μm) andcoarse mode (3.0~5.0μm).That shows the contribution of the sea salt in the aerosol.Atmospheric particulates over the China Sea are affected by land-sourced pollutant at thesame time. The number concentrations lower gradually with the offshore distanceincreasing.According to the number concentrations of particles in different size and thepublished particle density, mass concentrations are estimated from the year2010to2011.The results show that the mean particle mass concentration in Qingdao is167.7μg m-3,which is in agreement with the observed data. Number concentrations are in the law ofexponential decay after the dust events, so we offer a new model about dry deposition thatusing the data of particle number concentrations, and estimate the dry deposition flux. In2010-2011the atmospheric particle dry deposition flux in Qingdao is higher in spring(158.8mg m-2d-1) than in winter (144.2mg m-2d-1) and autumn (132.6mg m-2d-1), whichis the lowest in summer (78.5mg m-2d-1). Particle dry deposition flux over the China Seais42.7mg m-2d-1in May to June, and18.8mg m-2d-1in October.