| PM2.5, especially the sulfate, nitrate and ammonium in the PM2.5is well known to be associated with human health, air quality deterioration, and even global climate change. The primary objectives of this study include two sections. One is to assess two different real-time techniques for measuring SO42-, NO3-and NH4+in PM2.5by comparison with a honeycomb denuder filter-pack system in the much higher concentration condition in China. The other one is to investigate the water soluble ions of PM2.5combined with meteorological data and some of the gaseous precursors such as SO2, NOx and O3in Hong Kong from13October to14December in2010. The chemical compositions, temporal and diurnal variations, source apportionment of water-soluble ionic species in PM2.5were studied during the periods in detail. The conclusions were summarized as follows:The ambient ion monitor (AIM, URG9000B) showed good performance for NO3-and NH4+. The data of the AIM and the filter system agreed very well with regression slopes of1.00and0.91and a correlation coefficient of0.94and0.91, respectively. Another monitor for measuring aerosols and gases (MARGA, Model ADI2080), developed by ECN, Metrohm and Applikon, showed excellent performance for the measurements of SO42-and NH4+, with regression slopes of1.02and1.06and a correlation coefficient of0.96and0.96, respectively. But MARGA exhibited high NO3-measurement results, and accuracy of NO3-measurements should be evaluated further.AIM showed obvious overestimation for SO42-, which was attributed to the positive interference by high ambient SO2concentrations which could not be totally eliminated in the parallel denuder. To overcome this problem, an improved system including two denuders working in series and with the use of a new denuder liquid (5mmol/L H2O2+5mmol/L NaOH mixed solution) was used. The new system could absorb high concentration of SO2(even up to100ppb) so that the SO42-measurement results would not be affected. The total water soluble ions (TWSI) concentration in PM2.5of Hong Kong is in the range of5.54～74.66μg/m3, with the average of25.41μg/m3. SO42-, NO3-and NH4+, were the major secondary ions with average concentrations of14.25,4.86and2.93μg/m3, respectively. And the total of the three ions accounted for86.7%of TWSI.The diurnal pattern of SO42-and NO3-were similar with their precursor, SO2and NOx, which showed the sources of the secondary pollutants. Analyzing the relative between all the cations and anion, this paper demonstrate that the relationship between SO42-and NH4+was best, and R=0.84. The three main ions may exist in the form of (NH4)2SO4, NH4HSO4and NH4NO3. The average [NO3-]/[SO42-] was0.32, which is similar with the values of most cities in China.A principal component analysis showed that short-range and long-range transport of pollution, vehicle exhaust, sea salt and soil were the main factors affecting the variability of the measured ions.Analysis of two periods of pollution (Nov30-Dec2and Dec6-8) showed the concentrations of SO42-, NO3-and NH4+were16.02,6.45and6.14μg/m3, and20.98,7.58and3.56μg/m3, respectively. Good relationships between SO2and SO42-showed SO2was the main source of SO42-. Meteorological analysis showed that wind direction and wind speed had a significant impact on the status of air quality. The low wind speed would lead to stable weather and prevent pollution dispersion. Back trajectory analysis indicated the two air masses coming from different directions: one from Guangdong province, which led to high NO3-and NOx concentrations; another from north direction, which caused high SO42-concentration. |
PDF Full Text Request