| Being widely exist in soil, sediment, and even the polar atmospheric and alpinesnow, Black Carbon, with high thermal stability, is a kind of carbon materialproduced by biomass and incomplete combustion of fossil fuels. The source of blackcarbon aerosol can be divided into two kinds of source of natural and man-madesources. Black carbon aerosol can be used as cloud condensation nuclei to change thesize of cloud droplets distribution, cloud optical properties and the content of cloudliquid as well as the content of cloud cover. The researching of the clening efficiencyof black carbon aerosol of rainfall and its influencing factors, plays an important rolein the prevention and control of black carbon aerosol pollution.This study has analysed the concentration of black carbon aerosol and theconcentration of black carbon in a sample from May15,2013to January11,2014during the rainfall, with a purpose of learning the atmosphere removal efficiency andits mechanism of black carbon aerosol in the atmosphere in different rainfall time fordifferent seasons with different weather conditions and different rainfall intensity.The main results were as follows:(1) before the lake campus of rainfall during the Nanchang University totalsuspended particle (TSP) concentration range from21.32to216.21μg/m3, theaverage concentration of109.36±48.92μg/m3, which is not to exceed. Rainfall in theatmosphere during the BC concentration change range from0.16to13.86μg/m3, theaverage concentration of4.30±3.16μg/m3. Comparing with the domestic and foreigncities (not rain), the concentration of black carbon aerosol in Nanchang during rainfallis high and the pollution is serious,4.4times of Xiamen region,1.47times of theHangzhou,1.52times that of Nanjing,3.07times of the Swedish,5.8times that of themaximum level of Halifax, Canada,5.81times that of Atlanta，in US.(2) the black carbon aerosol concentration in atmosphere during rainfall inNanchang and TSP concentration are not apparently relavent.(3) the influencing factors of the black carbon aerosol concentration duringrainfall during in Nanchang: the concentration of black carbon aerosol in the atmosphere of atmospheric average concentration of black carbon aerosol presentedthe law of the high season, summer is low, the average concentration of3.74μg/m3insummer and autumn of2.75μg/m3, autumn and winter is5.4μg/m3, because summerrainfall frequency, black carbon aerosol concentration change is big, fall and winterand vice; During rainfall concentration of black carbon aerosol in the atmospherewith the increase of air relative humidity and present a diminishing trend, because indifferent rainfall, relative humidity is bigger, LWC is larger, which explains thecurrent situation there is a greater degree of rainfall and rainfall intensity, so theconcentration of black carbon aerosol in the atmosphere; During rainfallconcentration of black carbon aerosol in the atmosphere with the increase of airtemperature presented a decreasing trend, because the summer precipitation (hightemperature) more frequently and precipitation, black carbon aerosol in theatmosphere can be more flush to the rain, and the temperature rises, the aerosolparticles in Brownian motion in the air is also more intense, collisions with raindropscoefficient increases, increased rainfall on the removal efficiency of black carbonaerosol in the atmosphere, resulting in a loss of black carbon aerosol concentration inthe atmosphere during the rainfall.(4) the influencing factors of the black carbon in rainfall samples: rainfallsamples of black carbon aerosol concentration range of0.03~1.25(including μg/mL,average concentration of0.24(including μg/mL, suggests that black carbon aerosol inthe atmosphere trapped in rain samples; High rainfall BC average concentration in thefall and winter, summer is low; Rainfall and rainfall in a proportional relation withthe concentration of black carbon, large rainfall of black carbon aerosol in theatmosphere has more elution. But because of the high concentration of black carbonaerosol in the atmosphere has been a lot of scour at the early stage of the rainfall tothe rain, lead to the late rain, black carbon aerosol concentration in the atmospherehas been reduced, and the decrease of the late because of the rain the rain is strong,reduce the raindrops and the collision coefficient of black carbon aerosol in theatmosphere, these reasons led to large rainfall in the late of black carbon aerosol inthe atmosphere of the decrease of the flushing action, resulting in large rainfall duringrainfall in black carbon aerosol concentration range is not big; Rainfall in the electrical conductivity of the sample with the sample of black carbon concentration isdirectly proportional to have a good relationship, the reason is that black carbon dueto its structural characteristics, with strong adsorption ability, can effective adsorptionof organic pollutants and suspended in the atmosphere environment through rainfalltime has taken it to increase the complexity of the rain in the rain. Led to high rainfallsamples conductivity.(5) the influencing factors of the removal efficiency of black carbon aerosolrain: rainfall of black carbon aerosol clearance rate in the range of0.13%~6.68%,the removal efficiency of mostly below1%; Rainfall average removal efficiency ofblack carbon aerosol in the atmosphere represents a feature of low high summer,autumn and winter, and because the summer rainfall and rainfall intensity changerange is big, cause the summer rainfall during rainfall of black carbon aerosolremoval efficiency range than the autumn and winter; Black carbon removalefficiency and the present linear relationship between rainfall, studies have shownthat rainfall is less than40mm of rainfall of black carbon aerosol removal efficiencyis maintained at below2%, variation range of efficiency of0.13%~1.56%, when therainfall is more than40mm, the removal efficiency of black carbon aerosol began torapidly increase, rainfall, rainfall duration, rainfall intensity are cleared toatmospheric black carbon aerosol efficiency play a positive role, high strength, largeprecipitation rainfall erosion of black carbon aerosol in the atmosphere more useful;With the increase of conductivity, black carbon aerosol removal efficiency is alsoincreased gradually, but this kind of change rule is not linear; With the increase of airrelative humidity, black carbon aerosol removal efficiency is also gradually increase,presents the logarithmic relationship between, and when the atmosphere relativehumidity above90%(including90%), black carbon aerosol removal efficiencyincreased amplitude increase, when relative humidity increased from90%to96%, theremoval efficiency of black carbon aerosol increased from1.49%to6.68%, increasedby6%, and relative humidity of black carbon aerosol removal efficiency increased by5.19%. Visible when atmospheric relative humidity increased, more be helpful for theremoval of black carbon aerosol in the atmosphere; Cleared of black carbon aerosolrainfall efficiency as the basic temperature fluctuations in the same change trend, and within the scope of the temperature in the high, black carbon aerosol also at a higherrange of efficiency of rainfall, because at higher temperatures, rain and black carbonaerosol in the atmosphere of touch and strengthen, brown and black carbon aerosol inthe atmosphere of touch and the risk increased, led to the suspension of black carbonaerosol particles in the atmosphere more is washed by the rain drops to the groundsubsidence.(6) the influence on BC concentration and removal efficiency by continuousrainfall: in the selection of rain in more than two consecutive days, the black carbonaerosol concentration in a sample peaked in the first day’s rain sample, and then byday decline; Concentration of black carbon aerosol in the atmosphere as rain lateincreased gradually; Show of efficiency of black carbon aerosol day by day reducedregularity, this is because as the late rain, rain in black carbon aerosol in0.5~1μmdiameter of aerosol scour capability is reduced, thus it can infer, because black carbonaerosol in the atmosphere can be washed off in the early settlement has been the rainswashed out, so rainfall samples of black carbon concentration distribution for earlythan later; which leads to the decrease of removal efficiency on the black carbonaerosol by the rain. |
PDF Full Text Request