Measurements And Simulations Of Ozone And Its Precursors In Beijing

In recent years, large amounts of air pollutants were released into the atmosphere with rapid economic development in Beijing and its surrounding regions. This led to serious impacts on the atmospheric environment of Beijing. Photochemical air pollution is one of the serious environmental problems in Beijng. It is necessary to study the relationship between O₃ and its precursors.In this paper, we used multilayer observed data from Beijing 325-meter Meteorological Tower to analyze concentrations of O₃ and its precursors, including NO, NO₂ and CO, and the corresponding wind fields, temperature and other meteorological conditions from September to October of 2004. Characterized were O₃ vertical and temporal variations, and correlations with its precursors and weather conditions. A photochemical model was used to simulate O₃ concentrations before and after the cold frontal system and O₃ production rates were estimated by a simplified method and simulated by the constrained photochemical model. The findings and conclusions were summarized as follows:Peak O₃ concentrations usually occurred in the afternoon and concentration vertical differences were obvious in the boundary layer, the differences were small in daytime but large at night. The occurrence time of peak O₃ concentrations at 280 m was later and longer than that at 47 m and 8 m. SO₂ concentrations showed minor variations and its concentration at 47 m was higher significantly than at 8 m. NO_x and CO concentrations had typical daily changes, i.e., the lowest values occurred from 11:00 to 18:00 and the highest values from 21:00 to 23:00. Contrarily, so did O₃ concentrations. Daily NO concentrations had double peaks, one at about 8:00 and the other at 23:00. O₃ and CO had an obvious negative correlation. NO_xand CO also had a good correlation, and the correlation coefficient reached 0.6.By comparing observed data from Differential Optical Absorption Spectroscopy (DOAS) and from conventional measurements, we found that both had a nice consistency. O₃ concentrations were high under sunny and stagnant conditions. Strong wind and heavy rain caused by a strong cold frontal system (northerly airflow) can lower O₃ concentrations significantly but two-or-three-day persistence of sunny stagnant conditions after the cold frontal system may lead to high O₃ episodes. A photochemical model was used to simulate O₃ concentrations before and after the cold frontal system and simulations agreed well with observations. O₃ production rates were estimated by a simplified method and simulated by the constrained photochemical model. Both methods showed a nice agreement.