Characteristics Of Organic Acids And Inorganic Components In Three-stage Fog Water In Nanjing In Winter

It is a frontier topic in the field of fog research to study the drop size-dependent chemical composition of fog droplets,especially the composition of organic matter,through field observation.A 45-day field observation experiment was carried out in the northern suburbs of Nanjing in the winter of 2017.11 fog water samples were collected in Nanjing during December 30-31,2017 by using a three-stage Caltech Active Strand Cloud Collector?three-stage CASCC,cutting diameter:S1,>22?m;S2,16-22?m;S3,4-16?m?.Six organic acids,ten inorganic ions,p H and electrical conductivity?EC?were measured to identify chemical characteristics of fog water samples.The main conclusions can be drawn as follows:?1?A large amount of pollutants was enriched in three-stage fog samples in Nanjing.The trend of total ion concentration was basically consistent with the particle concentration.Back trajectories?72 hrs?showed that air masses impacting Nanjing during the observation period came from the sea and cities.The composition of fog water was mainly affected by ocean sources and anthropogenic sources in the surrounding area.Fog water composition was accounted for 87.91%of total ion concentration.Large contributions were observed by formate?HCOO^-?,methanesulfonate?CH₃SO₃^-?and oxalate(C₂O₄^2-)for total organic acids concentration.?2?The weighted mean volume concentration of both total ions and each species were size-dependent and enriched in small fog droplets?4-16?m?.The concentration profile was a‘‘U''-shaped curve.The mean ratio of SO₄^2-to NO₃^-was 1.18 and the range of that was0.85-2.34 in three-stage fog water,which was a mixed acidification of sulfuric acid and nitric acid.The acidification type of fog water in the northern suburbs of Nanjing has gradually changed from sulfuric acid type acidification to mixed acidification since 2006.?3?There were significant correlations between the concentrations of the four main organic acid ions in the three-stage fog water in Nanjing,indicating that the oxidation reactions that produce these organic acids occurred.The ratio of HCOO^-to CH₃COO^-concentration is low,with an average value of 0.392,indicating that the fog water was affected by the traffic sources on Ning Liu Road east of the sampling point.?4?The p H of samples,which were alkaline,ranged between 7.07 and 8.03.The slope of regression equation between potential neutralization and potential acidification was 1.15, reason for the significant decrease in acidity of fog water collected in 2017 compared with that of fog water collected in the same site in 2013 was the reduction of acid-causing components and the occurrence of neutralization reactions.?5?Comparing the ion composition of the three-stage fog water and the size resolved collected during the fog event,NO₃^-and SO₄^2-were the most important ions in the aerosol. particle-size aerosol.The fog process has a significant effect on the concentration distribution of ions in the aerosol.Comparing the chemical characteristics of fog water,rain water and snow water collected during the same observation in the winter of 2017,the acidity of precipitation is stronger but the pollution in fog water is more severe than precipitation.There is a difference in the characteristic ratio of ions between fog water and precipitation.