Atmospheric Nitrogen Pollution Chemistry In Qingdao And Its Main Influence Factors' Simulation

Along with the development of Qingdao city and the energy consumption structure's re-adjustment, the environmental problems of nitrogen and photochemical pollution caused by vehicle exhaust become more and more remarkable. Qingdao is a coastal city, located at the Asia-dust delivery access to the the Pacific Ocean. Two special kinds of aerosol (dust and sea-salt) could influence the atmospheric nitrogen pollution in Qingdao.By using the observational air pollutants data and meteorological data in Qingdao, the characteristic of it's air pollution and the relationship between NO_x and meteorological factors was studied. Based on the observational data, the mechanism of atmospheric nitrogen chemical conversion was simulated using the atmospheric chemistry module MECCA, and the influence of dust and sea-salt aerosol to atmospheric nitrogen chemistry process in polluted city was analyzed. By the experimental simulation of reducing the emission of NO_x, the effect of vehicle exhaust controlling was discussed. Main conclusions are as follows:â‘ The highest concentration of NO_x and COwas monitored in winter and the lowest in summer, while the variation trend of O₃ was on the contrary. The diurnal variation of NO_x showed two peaks in the dawn and dusk, higher in the daytime than in the nighttime. The peak valuef O₃ appears at noon. The ratio of NO₂/SO₂ was more than 1 in summer in both Qingdao and Beijing, which reflected that the pollution of NO_x was more serious in summer. The concentration of O₃ in sunny days was higher in the daytime than in the nighttime, but in cloudy and rainy days it's variation range between day and night was quite small. Time-delayed correlation analyzing shows that the cumulative effect time of NO_x on O₃ was about 5-6 hours. The concentration of NO_x was negatively correlated with temperature, humidity and average wind speed, but positively correlated with pressure.â‘¡An atmospheric chemistry module MECCA was used to investigate the influence of dust-storm on transformation of inorganic nitrogen-contained compounds,partitioning between the gas and particulate phase and deposition in polluted coastal atmosphere (Qingdao). Dust aerosols provided large surface areas to occur heterogeneous transformation of NO_x. These aerosols also reduced the solar radiation and indirect affected the NO_x transformation in the gas phase. It is found that the strong turbulent diffusion caused by the strong wind also played an important role on partitioning of N-contained compounds between the gas and particulate phases. The concentration of HNO₃ was influenced by NO_x in daytime, and by N₂O₅ in the night. The average concentrations of NO₃- and NH₄⁺ in coarse particles and NH₄⁺ in accumulation mode particles were 29.6μg/m3, 3.82μg/m3, 12.0μg/m3, respectively. When heterogeneous reactions enhanced with invasion of dust particles, the gaseous concentrations of NO_x,HNO₃,N₂O₅ and NH3 decreased(31.6%, 46.0% and 54.6%, respectively), and accompanied by the accumulation of NO₃- and NH₄⁺ in particulate phase (added 4.15 and 2.35 times). Reduce of solar actinic flux caused an increase of NO_x concentration, but did not influence NH3 and particulate nitrogen-contained compounds significantly. When the photochemical reactions in the gas phase and heterogeneous reactions were compared to each other, the photochemical conversion of NO_x in the gas phase dominated at the initial stage. After 24 hours, heterogeneous conversion of NO_x gradually enhanced and finally overwhelmed. When coupling diffusion loss into modeling, the concentration of NO_x and O₃ decrased but the concentration of aerosol nitrogen still increased.â‘¢The concentration of NO₂ in Qingdao and Beijing shows the same variation trend in daytime but was quite different in the night: the concentration of NO₂ shows a low peak in in the night Qingdao; while in Beijing, the value was higher in the nighttime than in the daytime. It was proved by the simulation experiment that the low concentration of NO₂ was mainly cause by the different chemical mechanism of sea-salt aerosol and nitrogen between day and night. Meanwhile, the different meteorological and geographic conditions between Qingdao and Beijing also were important influential factors to the variation of air pollutants.â‘£It was a efficacious way to reduce the urban air nitrogen pollution by decrease the vehicle exhaust. Theoretically, the concentration of NO_x will decreased to 50%～35% when the emission of NO decrease to 80%～50%. But in fact, meteorological condition was a very important factor that could influence the effect of vehicle exhaust's decrease. This was clearly proved by the comparative analysis on the two experiences of vehicle exhaust's decrease in Beijing.