Concentration Characteristics And Sources Of Bromine And Iodine In Aerosols

Study on chemical composition of aerosols, which can provide basic data for source apportionment of atmosphric particulate and heterogeneous reaction on particulate, is the basic research area. Bromine and Iodine are important reactive halogen species in the atmosphere, which can participate in many atmospheric chemical processes, play important role in the ozone depletion, affect sources and sinks of many important compounds. Reactive halogen chemistry is an important frontier research field in the atmospheric chemistry. Therefore, the aim of this dissertation is to develop a analytical method of iodine and bromine in coal and atmospheric particles, research concentration characteristics and sources of bromine and iodine in aerosols, and behavior of the trace elements bromine and iodine during coal combustion process.1. Determination of iodine and bromine in coal and atmospheric particles by inductively coupled plasma mass spectrometry. (1) 7-8 mL of nitric acid,1-2 mL of hydrofluoric acid, and 2 mL of hydrogen peroxide were used as digestion solution for coal, and for atmospheric particles,5 mL of nitric acid,2 drops of hydrofluoric acid, and 2 mL of hydrogen peroxide were used as digestion solution. (2) 5%(V/V) of nitric acid in determination solution was employed in this analytical method. (3) 1mL of NaS2O8(20% solution) and one drop of 0.1% AgNO3 solution were introduced in determination solution for oxidizing Br and I to the same valence. (4) The detection limits (DL) of Br and I were 5 ng/mL and 0.15 ng/mL, respectively. (5) The recoveries of Br and I ranged from 80% to 110% and from 80% to 120%, respectively. The accuracy of the method was well within the generally accepted range of 70-130% indicated in ISO 5725. (6) The determined contents of Br and I in soil certified reference materials by this method were accurate with comparison of certified value.2. Concentration characteristics of bromine and iodine in aerosols in Shanghai. (1) The contents of total Br and total I are 163.6±108.7μg/g and 55.6±37.7μg/g for TSP, and 230.4±137.0μg/g and 78.4±44.3μg/g for PM10, in sampling period, respectively. (2) The concentrations of total Br and total I are 27±20 ng/m3 and 9.4±5.6 ng/m3 for TSP, and 22±14 ng/m3 and 8.0±4.6 ng/m3 for PM10, in sampling period, respectively. (3) The seasonal variations of total Br concentrations in TSP and PM10 were Autumn> Spring> Winter> Summer. For total I, the seasonal variations in TSP and PM10 were Winter> Spring> Autumn > Summer. (4) The Br/I ratios are 7.0±16.5 and 5.3±9.6 for TSP and PM10, respectively. (5) For TSP, watersoluble Br and I accounted for 34±18% and 32±19% of the total Br and total I, while for PM10, water-soluble Br and I accounted for 31±18% and 32±15%, respectively. Soluble Br and I in PM10 extracted by acid increased by 22% and 18% respectively, compared with water-soluble Br and I. 3. The contents of Br and I in source dust of aerosols, and the behavior of bromine and iodine during coal combustion process. (1) The contents of Br and I in different coal are ranged from 10 to 30μg/g, and from 1 to 10μg/g, respectively. (2) The release of bromine and iodine increased with an increase in temperature, decreased with the increase of oxygen concentration. (3) At the given experimental condition, iodine was observed almost entirely in the vapor phase, but bromine was observed dominantly in the vapor phase, as well as in residue and particulate matter, respectively. (4) Solid additives could capture bromine and iodine effectively during coal combustion process.4. The sources and effect factors of Br and I in aerosols in Shanghai. (1) The sea water enrichment factor for Br ranged from 0.3 to 3.0, with a mean of 1.0±0.7, whilst for I, it ranged from 154 to 791, with a mean of 426±169 for PM10. It indicated that I concentrations were essentially affected by marine aerosol concentrations and the gas-to-particle reactions in the production of I aerosols. The major part of aerosols bromine originated from marine sources, and the bromine depletion on particulate surface was very high in summer and autumn. (2) When the wind flowed to the shore, the concentrations of particulate bromine and particulate iodine were lower than the values in the offshore flow. The wind direction, air pressure and air temperature were the major factors in influencing the concentration of Br and I in aerosols. (3) The concentrations of Br and I in aerosols increased with the concentrations of SO2 and NO2 increasing. Iodine in aerosols showed a highly positive correlation with SO2 and NO2, whereas for Br, it only weakly correlated with these pollutants. (4) When the air quality deteriorated, the Br/I ratio decreased. The Br/I ratio in aerosols showed a highly negative correlation with SO2 and NO2 in air.5. Iodine speciation in PM10. (1) The contents of iodate, iodide and soluble organic iodine(SOI) are 1.32±0.82μg/g,16.75±9.43μg/g and 18.23±11.06μg/g for PM10, during the day, respectively. The contents of iodate, iodide and SOI are 2.87±2.06μg/g,16.75±9.96μg/g and 24.21±11.46μg/g for PM10 during the night, respectively. (2) The concentrations of iodate, iodide and SOI are 0.24±0.22 ng/m3,3.36±2.21 ng/m3 and 3.67±2.67 ng/m3 for PM10, during the day, respectively. The concentrations of iodate, iodide and SOI are 0.24±0.22 ng/m3, 3.11±2.21 ng/m3 and 2.97±2.77 ng/m3 for PM10, during the night, respectively. (3) SOI and iodide are the most abundant fraction, accounting for 49.4±2.5%,47.1±2.4% during the day, and 42.7±11.5%,53.4±8.7% during the night, respectively.