上海市大气气溶胶中铁的来源和化学种态研究

Source identification and chemical speciation of iron in the aerosol particles in Shanghai City

利用扫描质子微探针对上海市室内外大气气溶胶和排放源的单颗粒进行测量,用人工神经网络识别技术追踪了各种排放源对这些气溶胶中Fe的贡献.结果表明,对于上海的开放空间、半开放的公路隧道和室内环境,各种排放源的贡献并不相同.还利用穆斯堡尔光谱研究了室内外大气气溶胶中Fe的化学种态.实验发现,室内外气溶胶中Fe的种态不尽相同,在人民公园和高架桥开放空间中主要是铁的硫酸盐,在半开放的隧道中主要是α Fe2O3,在室内主要是α Fe2O3(α FeOOH).Fe种态的转变不仅和大气中SO2有关,而且和空气中云雾等因素有关.

Aerosol particles (APs) have been extensively studied recently because they difference cause the poor visibility and adverse effects on health. The different size and speciation of aerosol particles cause the difference influences. Iron is one of the most large quantity elements in aerosol particles. Two suitable and lossless methods, SPM (scanning proton microprobe) and Mssbauer spectroscopy, had been used to identify the sources and speciation of aerosol particles from indoor and outdoor.Pollution source, such as construction dust, vehicle exhaust, coal and oil combustion, soil dust and metallurgical industry exhaust, of individual aerosol particles samples were collected. They were the major of the aerosol particles in Shanghai city. Three outdoor samples were collected to measure the total suspended particles (TSP): one was from a tunnel, another was from a viaduct side, and the other was from a park in the center of Shanghai City. More than 90% of the outdoor particles were smaller than 10 μm. Indoor samples of the fine particles were collected from the air conditioners at homes in five typical areas.The identification results showed that most APs in the park were derived from metallurgical industry exhaust, soil dust, and construction dust. Near the viaduct, metallurgical industry exhaust, soil dust, and vehicle exhaust contributed the most iron APs. In the tunnel, vehicle exhaust is the main source of iron APs. Those results were coincident with the local environment situation. The main iron sources of the indoor APs were same. But their contribution fraction had some differences. In average, the contributions of construction dust, metallurgical industry exhaust, soil dust, and vehicle dust were 35%, 35%, 27%, and 2.4%, respectively. All samples were measured with Mssbauer spectroscopies at RT and 80 K. Except the sample from the tunnel, there were no much difference of spectra between RT and 80 K. In tunnel, around 84% of iron was α-Fe_2O_3. According to the ratio of supermagnetic and ferromagnetic components at different temperatures, the size of α-Fe_2O_3 embedded in APs was around 10 nm. In indoor space, most iron in APs was α-Fe_2O_3 (α-FeOOH). The sizes of α-Fe_2O_3 in APs had two sets of values. The large one (>13 nm) that was considered major from soil dust. And the smaller one was thought from the smelter dust. In the open space (in the Park and near viaduct), most chemical state of iron was iron sulfate.The chemical state of iron in APs in open space was quite different from that in the tunnel and indoor space. SPM showed that iron mainly came from four different sources in the city. It was found that vehicle exhaust contributed 6% of iron in the total APs in the park. If iron still kept a state of α-Fe_2O_3 as in the tunnel, it should appear in the Mssbauer spectra. However, no spectrum with Mssbauer parameters related to α-Fe_2O_3. That can be assumed that most of α-Fe_2O_3 was converted to iron sulfate. The change of the chemical state might be caused through some chemical reaction during the aerosols migration. The sulfur dioxide could be chemisorbed at the gas-solid interface of APs, which existed in large quantity in Shanghai city. At functions of sunlight and water in fogs and clouds, it could be oxidized, and reacted with iron ions and iron oxide to form iron sulfate.