A Study On Developing On-line Measuring Systems For Chemical Components In Ambient Fine Particles And Their Real-time Variation In Guangzhou

Based on an improved particle-into-liquid sampler, two on-line measuring systems were developed to analyze water-soluble ionic components and organic carbon in ambient fine particles; and these systems have been used in studying the real-time and seasonal variations of these chemical components of fine particle at Guangzhou with regard to their sources and controlling factors. In addition to these, based on the real measurements, this thesis also proposed a measuring standard for haze weather and discussed the possible causes of the haze in Guangzhou. The major conclusions from this study can be drawn as follows:1. By assembling the particle-into-liquid sampler (PILS) with the instruments of capable to conduct rapid analysis, i.e. Ion Chromatography and Portable Organic Carbon Analyzer, two measuring systems were established for on-line analysis of ionic components and water-soluble organic carbon in the ambient fine particles, which were called as PILS-IC and PILS-TOC systems. Based on these systems, real-time concentration variation of water-soluble ionic components and organic carbon can be acquired rapidly and continuously. The comparison experiments between on-line measuring systems and off-line analysis on filter samples were conducted and the results show that, for both ionic compositions and organic carbon, the sampling efficiency ratios of on-line mearuring system to off-line filter sample analysis were 1.13 and 5.50 for the summer time, and 1.01 and 1.36 for winter, respectively. Obviously, the sampling efficiency of on-line system is higher than that of filter sampling method.2. Ionic components analysis of ambient fine partiles shows that SO₄^2-, NO₃^-, NH₄⁺ are dominated ionic components in PM2.5. Among these dominated ions, the mass concentration of SO₄^2- accounted for 60% and 54.6% of the total mass concentration of the five measured ions for the summer time and for winter, respectively. Moreover, average mass concentration ratios of nighttime to daytime are 0.46 for the summer time and 1.05 for winter.3. Real-time mass concentration variations of ionic components in PM2.5 were also being studied. The result shows that, in sunny weather of summer, concentration variation of SO₄^2-, NH₄⁺ and NO₃^- fit into following pattern: higher concentration in daytime and lower concentration in nighttime, while NO₂^- and Cl^- show lower concentration in daytime and higher concentration in nighttime. These suggest that photochemistry process may increase the concentration of SO₄^2-, NH₄⁺ and NO₃^-related aerosol particles, while depress the concnetration of NO₂^- and Cl^- related aerosols. However, these pattern were not applied to the days under raining and cloudy weather. Correlation analysis of these measured ions show that, NH₄⁺ and SO₄^2- has the highest coefficient of 0.85 during the summer time. The average ratio of NH₄⁺/ (2*SO₄^2-) is about 1.0 (the unit of concentration isμmol/L). This indicates that most of SO₄^2- in PM_2.5 are likely existing as (NH₄)₂SO₄. In non-haze weather during winter, real-time variations of the measured ions are similar to that of summer time, while under the haze weather condition, the real-time variation of the measured ions follows no pattern.4. The analysis of WSOC concentration in ambient fine particle show that the mean mass concentrations of WSOC in PM_2.5 and PM_1.0 are 29.6μg/m³ and 25.0μg/m³ during the summer time, respectively. This indicates that WSOC made up a significant composition of fine particles. While during the winter, the mean mass concentration of WSOC in PM_2.5 is about 13.2μg/m³, which is much lower than that in summer. Furthermore, the WSOC concentration ratios of nighttime to daytime in summer and winter are 0.65 and 0.91, respectively. It indicates that there is a higher variation in the WSOC concentration between daytime and nighttime in summer time.5. The real-time WSOC concentration variation shows that, during summer, the daily variation of WSOC concentration display a similar pattern as that ambient air temperature variation. This suggests that WSOC concentration in fine particles may largely controlled photochemistry reaction. However, this pattern does not applied to the winter time,. The correlation with theof weather conditions during the experiment period indicates that there is a positive correlation between the ambient air temperature and WSOC concentration in fine particle. This further demonstrate that the concentration of WSOC in summer is controlled by the photochemistry reaction or sun radiation. Moreover, wind speed and direction have less influence on the WSOC concentration. However, rainfall, especially heavy rainfall will dramaticly low the WSOC concentration in fine particle by the wash out of the ambient aerosols. During the winter, there is a much less positive correlation between the ambient air temperature and the WSOC concentration. The correlation betweet the weather conditions and the WSOC concentrationsuggest that daily variation of WSOC concentration during the winter may be affected by multi factors. Among these factors, the poor air flux will obviously resultes in the increase of WSOC concentration in ambient fine particles, while the cold air flow from north will significantly low the WSOC concentration.6. Based on the real-time mass concnetrion measurements of ambient fine particle in haze weather at Guangzhou, this thesis proposes to take the daily mean mass concentration of 90μg/m³of ambient PM_2.5as the numerical value of difining the haze weather condition. Furthermore, this thesis also discussed the causes of high frequency of haze weather in Guangzhou.