Emission Characteristics Of Chlorine Radical Precursors Of Disinfectant And Its Influence On Air Quality

The reaction of hydroxyl radicals（OH·）with nitrogen oxides and volatile organic compounds is the way to generate secondary pollutants ozone and organic aerosols.In addition to OH·,chlorine free radicals（Cl·）also have an important influence on the formation of secondary pollutants.The concentration of Cl₂ and Cl NO₂ in urban areas in China is relatively high.The importance of chlorine chemistry to air pollution in China has been confirmed by field observations.Chlorine-containing disinfectants have a wide range of applications.The HOCl and Cl₂ emissions from chlorine-containing disinfectants are easily photodegraded to produce Cl·and OH·,which may make important contributions to the formation of atmospheric chlorine chemistry and secondary pollutants.But research has rarely been reported.In this paper,we first constructed the emission inventory of chlorine-containing disinfectants HOCl and Cl₂;improved the chlorine chemical reaction mechanism in the numerical model CMAQ;used the WRF-CMAQ model to study the impact of HOCl and Cl₂ on the atmospheric environment.The thesis mainly includes three parts:1)Based on the bottom-up method,by establishing and improving the source inventory calculation method,constructing the HOCl and Cl₂ emission inventory of chlorine-containing disinfectants in normal conditions and during the epidemic period;2)Integrating the latest research results of the chlorine reactions mechanism,supplement the restrictive relationship between uptake coefficients and humidity,and improve the heterogeneous chemical reaction mechanisms in the carbon bond（CB）chemical reaction mechanism;3)Set scenarios based on the uncertainty of emissions and emit temporal,Using the WRF-CMAQ numerical model to study the impact of HOCl and Cl₂ on the air quality during the use of chlorine-containing disinfectants.The main conclusions are as follows:Based on the“bottom-up”emission factor method and material balance algorithm,the calculation method of HOCl and Cl₂emissions from chlorine-containing disinfectants,including 12 emission source categories,has been established and improved.The results show that under normal circumstances（2020.01）,HOCl and Cl₂ emissions are about 70 tons/day and 10 tons/day.37 tons/day from tap water disinfection,contribution to 45%of total emissions;domestic sewage disinfection 36 tons/day,44%;medical wastewater disinfection 7 tons/day,9%;cooling circulating water disinfection 2 tons/day,2%;environmental disinfection 1 tons/day,1%.The Yangtze River Delta,Beijing-Tianjin-Hebei,Pearl River Delta and Chengdu-Chongqing economically developed and densely populated regions have relatively high emission intensity.Shanghai,Beijing,Tianjin,Jiangsu and Guangdong provinces have higher emissions of HOCl and Cl₂ per unit area than 5×10^-2 kg/day·km².Uncertainty analysis with Monte Carlo model shows that the uncertainty range of total emissions is between-61%and 118%.The emission characteristics of HOCl and Cl₂ during the epidemic of large-scale use of chlorine-containing disinfectants.Although the anthropogenic pollutant emissions was greatly reduced.But large-scale environmental disinfection leads to emission of HOCl and Cl₂ from disinfectant was significant increased.Affected by the epidemic（2020.02）,the increase in HOCl and Cl₂ is about 27 tons/day and 4 tons/day,respectively.Among them,the emission of HOCl and Cl₂ in the disinfection process of domestic sewage,tap water,medical wastewater,and environmental sanitation increased by 11 tons/day,4 tons/day,3 tons/day and 13 tons/day,respectively.Contributions reached 35%,13%,10%and 42%respectively.The biggest changes are the environmental sanitation and medical wastewater disinfection processes.The emissions increased by 3300%and 35%compared to before the COVID-19 outbreak.Emission changes mainly occurred in the urban areas of the Yangtze River Delta,Beijing-Tianjin-Hebei and Jianghan Plain.The HOCl and Cl₂ emission intensity per unit area of Shanghai,Beijing,Tianjin,Jiangsu and Guangdong all increased by more than 2×10^-2 kg/day·km².Base on the carbon bond chemical mechanism（CB6r3）,this research is perfecting the chlorine chemical gas phase and heterogeneous reaction mechanism;and using the atmospheric numerical model WRF-CMAQ to simulate the impact of disinfection on atmospheric.If the epidemic does not break out,the HOCl and Cl₂from chlorine-containing disinfectants will cause the monthly average concentrations of HOCl,Cl₂,OH·,Cl·,1-h O₃,MDA8-O₃,and PM_2.5 to increase by 456 pptv and 52pptv,4.7×10³ molecule/cm³,2.1×10⁵ molecule/cm³,0.9μg/m³,1.9μg/m³,and 2.8μg/m³ respectively.After the COVID-19 outbreak,the monthly average concentrations of HOCl,Cl₂,OH·,Cl·,1-h O₃,MDA8-O₃,and PM_2.5increased by 620 pptv,73 pptv,5.4×10³ molecule/cm³,2.4×10⁵ molecule/cm³,1.8μg/m³,3.5μg/m³,4.4μg/m³respectively.The Yangtze River Delta and Beijing-Tianjin-Hebei and other densely populated,economically developed urban areas with high use intensity of chlorine-containing disinfectants are relatively more affected.Among them,the contribution of HOCl and Cl₂ emissions to the monthly average concentration of MDA 8-O₃ in Suzhou area is close to 10%,and the contribution to the monthly average concentration of PM_2.5is close to 5μg/m³;we should pay more attention to the impact of chlorine-containing disinfectants on the atmospheric environment.