Pollution Characteristics And Influence Factors Of Ozone And Its Precursors In Northern Rural Area Of Beijing

With the acceleration of Chinese industrialization and urbanization,the emissions of pollutants are getting worse.The problem of photochemical contamination characterized by ozone is becoming more and more prominent.As highly reactive gas,ozone has a negative impact on human health,the ecological environment and climate change.Many studies have shown that the atmospheric oxidation of our country is increasing and the regional characteristics of ozone pollution are obvious.The complex nonlinear relationship between ozone and precursors has brought great difficulties in studying the mechanism of ozone formation and pollution control.In order to explore the variation of ozone,the influencing factors of photochemical pollution and the pollution characteristics of precursors VOCs in the suburbs of Beijing over the summer,we carried out a 40-day synchronous field observation of meteorological elements,ozone and VOCs in the summer of 2016 in Huairou-the suburb of Beijing.And comprehensive analysis methods were used to analyze the observation data in detail.The main results of this paper are as follows:(1)The analysis of ozone concentration during the observation period used by statistical analysis method showed that suburbs are more prone to come up excessive ozone in Beijing in summer with the ozone concentration exceeded in 30%days and diurnal ozone concentration exceeded in 37.5%days during the observation period.The maximum of diurnal ozone appeared at 16:00,close with the time of peak value appeared in urban areas.Due to the increasing traffic volume in weekends of observation area,the concentration of ozone had a phenomenon of anti-"weekend effect".99 kinds of VOCs could be measured by TH_PKU-300 volatile organic compounds online monitoring instruments.During the observation period,the average concentration of VOCs was 18.25 × 10-9 of which NMHCs accounted for 53%;OVOC accounted for 28%.NMHCs consists of 73%alkanes,13%olefins and 14%aromatics respectively.The diurnal variations of VOCs showed that,the alkanes and aromatics had low diurnal concentration,and the differences between day and night was not obvious for Olefins,which resulted from the joint effects of daytime plant emissions and photochemical reactions with higher concentrations of aldehydes and ketones.(2)To explore the effects of meteorological factors and inorganic gaseous precursors on ozone,the variation law of ozone concentration during the ozone heavy pollution was analyzed emphatically,and the source of air mass during heavy pollution was analyzed using the trajectory of the backward airflow.The results showed that the specific causes of different ozone-pollution process are different,and the observation area was affected by transmission of urban smoke and regional photochemical pollution.Combining the data analysis of multi-site ozone data,we found that ozone showed an obvious transmission characteristics in the southeast.Higher ozone concentrations appeared in daynight,which is influenced by meteorological conditions.The ratio of p-xylene/ethylbenzene is used to represent the photochemical age,and the relationship between ozone and photochemical age showed that the formation of ozone increasing with the increase of photochemical age.(3)The sensitivity of ozone was analyzed basing on the observed data in this paper.According to the ratio of VOCs/NOx,the photochemical sensitivity of ozone could be judged preliminary,and the results showed that the relationship between VOCs/NOx and ozone was different during ozone pollution period and no-pollution period.Besides,ratio of VOCs/NOx indicated the chemical sensitivity in the morning.The effective OPE of 22 d was obtained by the method of ozone production potential(OPE),and the probability of occurrence of NOx control zone and VOCs control zone was equal(41%).The OPE have proven especially fruitful in judgment of photochemical sensitivity of ozone in pollution period,and photochemical sensitivity can be changed in the process of photochemical reaction in the ozone heavy pollution period,NOx emission control area(NECA)gradually changed to VOCs emission control area.(4)The reactivity of VOCs was investigated by LOH and OFP,and the proportion of olefins was the largest in LOH,While in OFP it was aromatic hydrocarbons.The chemical loss of diurnal VOCs(except for isoprene)and the actual atmospheric concentration ratio was 1:7 based on the estimation of the photochemical age of the air mass.The chemical loss was 0.54× 10-9 using concentration of isoprene products,which is larger than that of other VOCs.The observation area is far away from the emission source and the influence of the industrial source is relatively smaller than traffic source judged by the feature ratio method.The source of n-alkanes analyzed by carbon dominance index showed that anthropogenic sources have a greater impact on them.The source factors of plant source,biomass burning,petrochemical industry,motor vehicle emission and solvent volatilization Were analyzed by PMF model and their contribution rate was 12.73%,18.96%,16.07%,38.63%and 13.6%respectively.The contribution rate of motor vehicle emission and solvent volatilization is increasing on ozone pollution days。...