Study On The Wind-driven Diffusion Characteristics Of Pollutants From Prescribed Burning For Crop Residues

Open field burning can efficiently dispose of crop residues in rural areas.Severe haze was often produced due to the open field burning,releasing large amounts of air pollutants to surrounding areas driven by wind,which would severely threaten people’s physical and mental health.Hence,there is certain practical significance to study the diffusion characteristics of pollutants from crop residues burning driven by wind fields to effectively guide prescribed burning to dispose the crop residues,reducing the urban air pollution and promoting the sustainable development of urban environment and agricultural production.This paper establishes a regional meteorological and air quality simulation method based on the Weather Research and Forecasting（WRF）and the Community Multi-scale Air Quality（CMAQ）simulations,and thereby different burning schemes are designed as prescribed burnings in Tailai County,to study the diffusion characteristics of pollutants from prescribed burning for crop residues of wind-driven.The main contents are included as follows:（1）Based on WRF-CMAQ simulations combined with Multi-resolution Emission Inventory for China（MEIC）and a regional coupled chemistry and meteorology simulation method is established.Both meteorological and environmental data were utilized in this study for validation.Study results indicate that the meteorology and pollutant concentrations simulations agree very well with the data from the monitoring sites.For meteorology,the correlation coefficient（R）of simulated wind speed reached 0.78,wind direction reached 0.9,and temperature and relative humidity reached 0.95 and 0.83,respectively.Meanwhile,the maximum mean error（MB）of wind speed was 0.67 m/s,the MB of wind direction was-8.9^o,and the MB of temperature and relative humidity was-3.72 ^oC and 3.61%,respectively.For pollutant concentrations,the R of PM₁₀ and PM_2.5 reached 0.71 and 0.78,respectively,with MB of-15.41 and-6.97μɡ/m³.（2）The method is established about localized crop residues burning emission inventory allocation by using the local survey data and the crop residues production in the study area was counted,among which crop land is the very type used as the weighting indicator above.Emission inventory has been established within the scope of crop residues burning in this study,and combined with the WRF-CMAQ air quality numerical simulation method to analyze and study the impact of straw burning on regional air quality.Study results prove that crop residues burning caused pollution to regional air quality,and the degree of pollution is mainly related to the wind field（wind speed and direction）,burning ratio,burning time-window and distance from burning area.The burning ratio increases and the concentration of air quality pollutants also increases in the surrounding area under the same meteorological wind field conditions.The shorter the burning time-window is,the shorter the duration of pollution lasts,and the more serious of the urban is polluted.（3）According to the pertinent factors influencing the diffusion of pollutants from crop residues burning to design different burning scheme as prescribed burning,emission inventory has been established within the scope of crop residues burning.The diffusion characteristics of pollutants from crop residues burning driven by wind field were analyzed by air quality simulation in the burning area.Study results indicate that the peak concentration increments of PM_2.5 is linearly and negatively correlated with the local wind speed,and only regions on the downwind path of the burning area would be influenced by crop residue burning,the regions in other directions are seldom influenced.The peak concentration increments of PM_2.5 is linearly and positively correlated with the burning ratio.The duration of urban pollution is related to the burning time-window,and the longer the burning time is,the longer the duration of pollution lasts.Meanwhile,the increment of peak and average concentrations of urban PM_2.5are positively related to the distance of burning,and the earlier the city is polluted and the earlier the incremental peak concentration of PM_2.5 is reached.