Relationship Between The Characteristics Of Precipitation And Air Quality In Nanjing

Nowadays,acid rain is one of the worldwide environmental problems.Generally speaking,the rain with pH value less than 5.6 of the rain,snow or the other forms of precipitation is called the acid rain.The main pollutants,like SO2,NO2in the air,are the mainprecursors of sulfate ions and nitrate ions in precipitation.PM2.5 is the particulate matter suspending in the air of which the aerodynamic equivalent diameterisless than 2.5 microns.Nanjing,the capital city of Jiangsu Province,is located in the Yangtze River Delta.With the economic development and the acceleration of urbanization,the atmospheric pollution problems become more serious and complex.In order to understand the relationshipsbetween acid rain pollution,the status of the precipitation characteristics and the major pollutants in the air of Nanjing,we analyze the monitoring data of precipitation and the automatic monitoring data of air of Nanjing in 2013from different point of view in this thesis.Meanwhile,with the trend analysis of the data from 2009 to 2013,we have got the variation of the past five years of acid rain pollution and air pollution.All these can help us further study the relationship between the precipitation and the air quality.The main conclusions are as follows:1.The average precipitation of Nanjing in 2013 was 864 mm and monthly precipitation was inverted V type.The order of the precipitation from high to low was:summer,spring,autumn and winter.The average pH of the precipitation was 5.13 and that of the acid rain samples was 4.72.The PH value of single sample precipitation ranged from 3.52 to 7.88,with the minimum value in May and the maximum in August.The precipitation pH values have been less than 5.6 for five consecutive years and it means the precipitation in Nanjing city is weak acidity now.The rank correlation coefficient of the precipitation pH and acid rain pH are-0.9 and-0.8,which shows that in Nanjing City,the precipitation acidity and acid rain acidity are increasing obviously year by year.2.In 2013,the acid rain rate of Nanjing was 35.6%and Nanjing became to be the acid rain prone area.Most of the acid rain pollutions in Nanjing were weak acid and acid rain,accounting for 71.4%of the samples.The second was the heavy acid rain and serious acid rain occurred occasionally.The most serious acid rain pollution happened in winter,when the incidence rate of acid rain was the highest,also with the strongest precipitation acidity and acid rain.The incidence of acid rain is inversely proportional with the pH value.The smaller the pH value of precipitation is,the higher the incidence of acid rain is,which means the higher the incidence of acid rain is,the stronger the precipitation acidity.On the contrary,the greater the pH value of the precipitation is,the smaller the incidence of acid rain is,i.e.the smaller the acidity of precipitation is,the lower the incidence of acid rain.For five consecutive years of acid rain rate over 30%,the rank correlation coefficient was 0.7,which indicated the incidence of acid rain in Nanjing increased year by year,but not significant.3.The equivalent concentration of ions in precipitation samples in Nanjing in 2013 is 680 ?eq/L.Theions concentration from high to low was:Ca2+>SO42->NH4+>Cl->NO3->Mg2+>Na+>K+>F-and that of SO42-/NO3-is 2.3.The air pollution precursor which influenced precipitation characteristics of Nanjing was still SO2.The average value of SO42-/NO3-in five years was 2.5,indicating that sulfate ion was still one of the reasons that caused acid rain in Nanjing.There is a certain relationship with the concentration of SO2 in the air.The acid rain in Nanjing is mainly caused by soot combustion pollution.However,according to the rank correlation coefficientof SO42-/NO3-,rs=-0.6 shows the SO42-/NO3-ratio decreased gradually.That is to say the influence of precipitation from the precursor NO2 becomes larger and larger.The acid rain pollution from coal-burning type oriented is transforming to mixed coal smoke and vehicle pollution gradually.4.In 2013,the annual average concentration of SO2,NO2,PM2.5,PM10 in the air in Nanjing were 37,55,78 and 137 ?g/m3.In accordance with the ambient Air Quality Standards(GB3096-2012),all the pollutants exceeded the standard except the annual concentration of SO2,NO2 exceeding the standard 37.5%,PM2.5 over 1.2 times and PM10 nearly 1 time.According to the monitoring data of Nanjing in the past five years,SO2,NO2 and PM10 concentration shows the pollution was lighter in summer and heavier in winter.The variation of SO2 and NO2 was consistent,wit flat type V.Because of the influence of dust and the burning of straw,PM10 may rise in the specific period,for example:in March,April,June and November.5.The average concentration of SO2,NO2,PM10 and PM2.5 in the non rainfall days is higher than that in rainfall days.The precipitation affects heavily on SO2,decreasing by 40%compared with the non rainfall days.The effects on PM2.5 and PM10 are about 30%,while that on NO2 is 19%.Whether it is light or heavy pollution,precipitation can purify the air pollution to different degrees.With the precipitation less than 5 mm,precipitation purification has little effect on particles in the air,which may even lead the hygroscopic growth of particles and cause the increase of the concentration of particulate matter.When the rainfall is moderate,the purification rate of precipitation on PM2.5 is usually less than that on PM10.When the rain is heavy,the purification rate on PM2.5 and PM10 was above 70%.In heavy pollution days,the purification effect on NO2 is not so obvious and the concentration is still high even after a heavy rain.6.Through the analysis of the selected samples of PM2.5,the concentration of PM2.5 after the rain was lower than that before and in the rain in autumn and winter.Of which the change is obvious.But in summer,the concentration of PM2.5 is relatively low and even if it decreases,it is not obvious.What's more,as the humidity is bigger in spring and summer,PM2.5 usually comes to a hygroscopic growth.With the increase of the concentration of scouring time rain,the concentration of PM2.5 will have a certain decline.The water soluble ions of PM2.5 are almost the same in the precipitation in Nanjing.Precipitation also has the effect on cutting down the water soluble ions of PM2.5,obviously on the SO42-,NO3-,NH4+,Cl-and K+.The average proportion is between 30%and 50%.By the analysis of samples before and after rain,the scouring effect on the water soluble ion concentration of PM2.5 in spring and summer is much lower than that in winter and autumn.Sometimes the concentration of SO42-,NH4+,NO3-after rain is higher than that before rain,which is concerned with not only the low concentration of gaseous pollutants in spring and summer,but also the uniform distribution.In the winter and autumn of 2013,Nanjing suffered heavy air pollution because of fog and haze weather and the burning of straw in eastern China.Meanwhile,the concentration of PM2.5 in the air was very high.However,both the concentration of PM2.5 and the water soluble ions in PM2.5 sharply declined after rain.