| NH3,as an important alkaline gas in the atmosphere,can neutralize the acidic substances in the atmosphere to produce ammonium salts,ammonium salts can reduce atmospheric visibility,affect regional ecosystem balance.In this study,Nanchang mixed area,road area and Changbei suburb sampling area have been taken for the monitoring area,by using Nessler's reagent spectrophotometric method to measure NH3,particulate matter and rain water NH4+ concentration to explore the formation mechanism of ammonium salt and efficiency of precipitation on ammonium salts.The main conclusions are as follows:?1?In the new urban area of Nanchang,the mean NH3 concentration was 49.17?g/m3,the mean NH4+ concentration in PM2.5 was 17.98?g/m3.Both of values were higher than that in other areas,indicating that Nanchang NH3 and NH4+ in PM2.5 pollution is serious.?2?In spring,the concentration of NH3 showed the result that suburb>road area>mixed area;NH4+ concentration showed road area> suburbs> mixed area.In summer,NH3 concentration showed suburb>mixed area>road area;NH4+ concentration showed suburbs> road area> mixed area.It was suggested that the distribution of NH3 concentration was related to the emission source,and the NH4+ concentration distribution was related to the formation mechanism.?3?In the front lake school zone ambient air,the NH3 concentration had a seasonal prevalence difference: spring>autumn>winter>summer.The NH4+ concentration in PM2.5: autumn>winter>spring>summer.This is because the different meteorological conditions in each season had a great impact on NH3 and NH4+ concentration distributions.In the spring,summer and autumn seasons,the NH3 concentration daily distribution characteristics showed that NH3 concentration in daytime was lower than that in nighttime,for winter,the condition was exactly the opposite,indicating that NH3 concentration was mainly affected by the night inversion during spring,summer and autumn three seasons;while in winter,mainly by temperature.The daily distribution characteristics of NH4+ concentration in PM2.5 were different in each quarter,the NH4+ concentration was relatively stable all day except for lower concentration during 7-9 in spring;the daytime NH4+ concentration was lower than that during nighttime in summer,the situation was opposite for autumn and winter;indicating that spring nighttime accumulation was balanced with daytime generation;In summer,the amount of production was higher than the cumulative amount,the condition in autumn and winter was the opposite.?4?According to the backward trajectory analysis,the ammonium salt in PM2.5 of Nanchang was mainly influenced by local sources,field sources had a little effect on the formation of ammonium salt in PM2.5 during spring and summer of 2014;in autumn,field sources played a more important role.In winter of 2015,NH4+ in PM2.5 was mainly due to the accumulation of local sources.?5?The ratio of NH3/NH4+?mean 5.47?was a bit large,showing that conversion process of NH3 to NH4+ was slow and the conversion amount was less than the amount of NH3.The seasonal distribution of NH3/NH4+ ratio was spring> summer> autumn> winter,by the both influences of NH3 and NH4+ concentration distribution.The ratio of NH3/NH4+ in daytime was higher than that in nighttime for spring,summer and autumn;the condition was opposite in winter as same as the NH3 concentration daily distribution characteristic.The spatial distribution characteristics of NH3/NH4+ ratio was suburbs<road area<mixed area,indicating that the conversion of NH3 to NH4+ was strongly influenced by the precursors SO2 and NOx concentrations.?6?Through the correlation analysis among the factors,conclusions can made that the change of ammonium salt concentration in was influenced by the concentration of NH3,SO2 and NO2 in the PM2.5,and the formation process was related to the temperature and humidity.There were mainly ammonium sulfate and less ammonium sulfate in Nanchang ammonium salt,in some of the particles,there were more ammonium nitrate,in addition to other forms existing,such as ammonium chloride,organic amines,etc.?7?Nanchang university rainfall pH average value was 5.41,generally acidic;in the process of segmental rainfall,the pH had a upward trend from April to June,indicating that the H+ in Nanchang from April to June mainly came from the under cloud scouring,the in cloud clear contribution was small,it's opposite in November.The change trends of fractional rainfall conductivity and NH4+ concentration were roughly the same,which showed that the rainfall values were relatively large at the beginning of rainfall,then decreasing rapidly,and then maintaining the relative temperature,and then gradually having a rebound in the later stage of rainfall,indicating that the initial rainfall had an obvious removal effect on total ion and NH4+,most of the ions in the rain come from the under clouds washing.?8?The scavenging efficiency of NH3 of rainfall was 2.44%72.06% and the average was 42.44%.The scavenging efficiency of NH4+ in PM2.5 of rainfall was 27.23%76.22% and the average was 42.44% and that in TSP was 27.23%76.22%,the average was 53.83%,the results showed that the removal efficiency of NH4+ was higher than that of NH3;On a continuous rainfall day,when the rainfall was large,the NH3 concentration decreased rapidly,when there was no rainfall or rainfall was very small,NH3 concentration recovery was also faster;while NH4+ concentration showed a high value before the first rainfall,and then washing down by rainwater,then decreasing rapidly and then maintaining at a low concentration level.In the absence of rainfall,the concentration increased slightly,indicating that continuous rainfall had strong inhibitory effect on NH4+ concentration in air,weak inhibition on NH3 concentration. |
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