| Haze pollution is an atmospheric phenomenon with visibility less than10km dueto complex material suspended in the air, such as dust, smoke and other fine particles.Despite the adverse health effects in humans, haze particles can change the radiationbalance of the earth, damage forests and crops. Dust pollution is a phenomenon withgreat amount soil dust blowing to the atmosphere by winds which caused by landdesertification and other reasons. Water-soluble calcium, magnesium ionsconcentrations in atmospheric particulate matters increased significantly during dustpollution episodes. Additionally, dust could also be transported to the downwindurban areas with strong airflow. The trace gases emitted in the urban areas catalyticreacted by the metal in dust, which will aggravate the haze pollution. Therefore, thecombination of natural and anthropogenic sources is one of the main reasons of hazein recent years.The main compositions of the haze and dust include sulfates, nitrates, ammonium,calcium and magnesium ions, etc. accounting of30to60%for mass concentrations infine particulate matter (PM2.5). Sulfates and nitrates are primarily from the conversionof SO2and NOxby chemical reaction which emitted from fossil fuel combustion.Calcium, magnesium, sodium and potassium are mainly from the dust sources. Bymeans of the observations of the water-soluble inorganic ions of particles in the hazeand dust, the interaction of human activities and natural ecosystems can be analyzedin detail, which will provide scientific information for the formulation of theecosystem and water conservation measures.To understand real-time variations of the mass concentrations of water-solubleions in atmospheric haze and dust particulate matters, a rapid collection of fineparticles and ion chromatography system (RCFP-IC) was designed and developedindependently by Beijing Institute of Atmospheric Physics, Chinese Academy ofSciences. Using this system, the mass concentrations of water-soluble ions weremeasured. Major conclusions can be drawn as follows.1. The typical haze pollution episodeA heavy atmospheric pollution was observed in Beijing from February18to24,2011. In this heavy pollution period,91%of the total water-soluble inorganic ionmass concentration was contributed from NO3-, SO42-and NH4+, leading to a relativelylow visibility. The temporal trends of Cl-and K+were similar to the trend of PM2.5. Incontrast trends of Mg2+and Ca2+were different form secondary ions. Aerosol pH andatmospheric oxidation rate studies have shown that in heavy haze pollution, aerosol inwinter was acidic and particles generated with heterogeneous chemical reactions. Thesources of water-soluble ion analysis showed that pollution came mainly from localpollutant emissions and the surrounding contaminated areas transportation.Water-soluble ions could be divided into three categories:1) gaseous precursor ions,2)fossil fuel combustion-related ions.3) soil source ions.2. The typical dust seasonIn March2011, when typical dust pollution usually occurred, one-month continuous observation of water-soluble ions was performed. Five pollution episodeswere observed during the study period. All ions measured had similar temporalvariations showing saw-tooth cycle with slow accumulation and relatively rapidclearing. Ca2+, the dust characteristic ions monthly mean value reached11μg m-3,and the highest value reached87μg m-3. In five pollutions in the observation period,Mg2+/Ca2+ratios had2different values which indicated dust particles in dust seasonwere from2different sources. One was long-distance transmission, the other waslocal blowing. Sources analysis of water-soluble ions in dust season showed that thenorthwest cold front arrived in Beijing cyclically brought more soil source ions toBeijing. In dust season, the dust characteristic ions accounted for60%of PM2.5, whilethe secondary ions only accounted for40%of PM2.5.3. The typical haze-dust combined pollution episodeDuring haze-dust combined pollution episode, both fine and coarse particlesincreased substantially. In fine particles, the polluting ions increased earlier than thedust ions in the compound pollution, but the ions of dust in fine particles part continueaffected atmosphere after the peak pollution. |
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