Observation and Analysis of Taizhou Atmosphere NH3 Concentration by Off-Axis Integrated Cavity Output Spectroscopy
ZHANG Guo-xian1,2, HU Ren-zhi1*, XIE Pin-hua1,2,3,4, WANG Feng-yang1, WANG Yi-hui1,2, TONG Jin-zhao1, CHEN Shi-yi5, LI Shu-le5, QIU Wan-yi5, LIU Wen-qing1,2,3,4
1. Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
2. Branch of Graduate School, University of Science and Technology of China, Hefei 230026, China
3. CAS Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361000, China
4. College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
5. State Key Joint Laboratory of Environment Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
Abstract：Ammonia (NH3) is the most important reduced form of active nitrogen in the atmosphere, and is an important gaseous precursor for the formation of secondary inorganic ammonium salts. Under the extremely polluted conditions in China, these ammonium salts can account for 40%～60% of the mass of PM2.5. NH3 pollution not only affects the intensity of light radiation globally but also exacerbates atmospheric photochemical pollution. At present, the source of ammonia in urban areas is still controversial. In order to study the pollution of NH3 in Taizhou, and then determine the source of NH3. Based on the off-axis integrated cavity output spectroscopy technology, this paper carried out continuous observation of atmospheric NH3 concentration in Taizhou in summer. Other pollutant concentrations (such as O3，NOx，CO，NH+4) were measured simultaneously. The observation point is 300 m away from the traffic arterial. The average concentration of NH3 during the observation period is (25.1±4.5) μg·m-3, which was higher than that of other cities at home and abroad. There is no significant difference in the mean value of NH3 during the day and at night, but it generally decreases during the day and increases at night. The stable atmospheric boundary layer at night maybe one of the main reasons for the accumulation of pollutants. In the morning, the concentration of NH3 increased sharply, mainly due to the evaporation of NHx(gaseous NH3 and particulate NH+4) deposited in water vapor at night. With the enhancement of light, the evaporation of NHx in environmental water vapor gradually ended, the photochemical reaction process gradually began to be dominated, then NH3 concentration increased slowly, gradually reached equilibrium, and finally declined rapidly. When the humidity at a high level during nighttime, the deposition process of NHx is easier to observe. They are combined with the meteorological parameters during the observation period and the concentration with the concentration of the conventional pollutants. The trend and level of pollutants in the Taizhou area has been discussed. The results show that the impact of traffic emissions on the NH3concentration in Taizhou is small on most days. Only June 7th, NH3 has a good correlation with NOx，CO, with R2 of 0.740 and 0.911. It is speculated that the day’s traffic has a significant influence, and the traffic source is an important local source of NH3. Backward trajectory analysis was performed to compare the changes in pollutant concentrations caused by different air masses during the observation period. According to the analysis of observation results, pollution discharge from the industrial area on the northwest of the observation point may be an important cause of the pollution incident on June 10th at night.
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