| Nitrogen cycle and sulfur cycle are very important contents of biogeochemical circulation, and the gas to particle conversions of sulfur and nitrogen in aerosol have long been a critical subject of the study. The measurements were carried out on the campus of Taiyuan University of Science and Technology, Taiyuan. High Volume Cascade Impactors Model TH-1000 and TE-235 were used for sampling PM2.5 and size segregated aerosol particles from May 2013-April 2015. At the same time, the corresponding atmospheric SO2, NO2, O3, meteorological parameters were recorded. Based on the data mentioned above and the level of water soluble ions（SO42-, NO3-, NH4+）, the level and distribution of sulfur and nitrogen conversion ratios（Fs and Fn） were got and the influences were discussed. Results showed:（1）The SO2 and NO2 contents were 89.98 μg·m-3 and 64.73 μg·m-3 in summer（2013）, respectively, while NO2 level was constant in winter（2013）, but SO2 increased to119.09 μg·m-3 due to higher coal combustion for heating. The SO42- and NO3- levels in PM2.5 were 16.54 and 6.87 μg·m-3 in summer, and obviously decreased to 12.79 μg·m-3 and 5.53 μg·m-3 in winter, respectively. By using the modified forms of the gas-particle distribution, Fs and Fn were 0.13 and 0.08 in summer, and 0.07 and 0.06 in winter, respectively.（2）The SO2 contents in winter（2014）was high to 182.79μg·m-3, which was sixth times to that in summer（2014）, while NO2 remained constant. SO42-, NH4+ mainly existed in particles of size < 0.95μm, and NO3- had almost the same unimodal size distribution with SO42-, NH4+ in winter（2014） and spring（2015） that there was a slight peak in size 0.3-7.2μm in summer（2014）. Fs were 0.39, 0.07 and 0.24 with almost unimodal size distribution separately in summer, winter and spring. Fn were 0.20, 0.14 and 0.18 in corresponding season. Both of Fs and Fn were much higher in size < 0.95μm, while Fn also had a peak in coarse mode of 3.0-7.2μm.（3）Both Fs and Fn were affected by multiple factors simultaneously, and the main factors varied seasonally. This study showed the temperature was the very important factor. SO42- and NO3- in PM2.5 mainly came from the homogeneous gas-phase reaction, however in winter（2013） SO42- maybe partly come from the heterogeneous reaction and that was the mainly path of Fn. Later, the analysis gained that the sulfur and nitrogen conversion were more likely to occur in the fine particles through heterogeneous reactions. The sulfur conversion may be complicated in summer that photooxidation, homogeneous gas phase and heterogeneous reactions occurred at the same tame. The conversions in fine and coarse mode independent from each other and NO3-in coarse mode came from the reaction between nitric acid and soil particles. Influences of gas to particle conversion of sulfur and nitrogen in size segregated aerosol particles were so much as temperature（T, °C）, relative humidity（RH, %）, O3, the density of fine particles, and the Influences were more obvious in typical weather.（4）Dates got from PM2.5 and size segregated aerosol particles indicated that SO42-, NO3-were fully combined by NH4+ and the gas ammonia was enough which may enhance the gas to particle sulfur and nitrogen migration and conversion. What`s more, the chemical components（eg. OC, EC） and larger particle surface area per unit volume enhanced the nitrogen conversion, especially in winter, and acted little on sulfur conversion in Taiyuan.（5）This paper discussed Taiyuan as a local-regional system. About 24% sulfates（calculated according to the sulfur element） were translated from sulfur dioxide produced by the system and were almost removed by wet deposition. About 17% nitrates（calculated according to the nitrogen element） were translated from nitrogen oxide produced and about 35% were removed by wet deposition（take up 6% of the nitrogen oxide）, while about 3% were removed by dry deposition. Parts of the rests either were detained or transferred remotely to other places through atmospheric circulation. |
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