| Real-time measurements of PM2.5, secondary inorganic compounds in PM2.5 (SO2-4, NH+4, and NO-3) and related gaseous pollutants were conducted at Mount Dinghu, a regional background station of the Pearl River Delta (PRD), in October and November 2008 by using a conventional R&P TEOM and a system of rapid collection of fine particles and ion chromatography (RCFP-IC). Sources and transportation of atmospheric particles during the experiment were discussed with principal component analysis and backward trajectories calculated using HYSPLIT model. The average daily mass concentrations of PM2.5 were 76.9 μg·m-3 during sampling period, and average daily mass concentrations of SO2-4, NH+4, and NO-3 were 20.0 μg·m-3 , 6.8 μg·m-3 and 2.6μg·m-3 , respectively. The sum of these three secondary inorganic compounds accounted for more than one third of the PM2.5 mass concentration, which had become the major source of atmospheric fine particles at Mount Dinghu. The diurnal variation of PM2.5, SO2-4, and NH+4 all showed a “bimodal” distribution with two peaks appeared at 10:00 am and at 16:00 pm, respectively, whereas NO-3showed “single peak” distribution peaked at 10:00 am. The mass concentrations of SO2-4 in PM2.5 had the similar diurnal variation with that of SO2, SO2-4 in PM2.5 was mainly transformed from SO2, whereas NO-3showed difference diurnal variation with that of NO2, and the second conversion rate of NO2 was far lower than that of SO2. NH+4 in PM2.5 existed mainly in the form of sulfate, nitrate and chloride. Both of principal component analysis and back trajectory analysis showed that the variations of PM2.5 and secondary inorganic compounds at Mount Dinghu were mainly affected by the long-range transport air mass passed over Guangzhou, Huizhou and other highly industrialized areas which carried air pollutants to the observation site, at the same time local sulfate originated from secondary formation also contributed an important part of atmospheric fine particles and the contribution from local direct emission was little. |
