| In recent years,air pollution has become one of the most severe environmental problems affecting human daily life.Affected by the types of pollution sources,emission intensity and distribution,topography,weather conditions,and meteorological factors,there are differences in the characteristics of pollutant concentrations in different regions.As a transitional zone between arid and humid areas,semi-arid areas are extremely sensitive to changes in climate change,and their air pollution characteristics are unique.Therefore,in-depth analysis of the characteristics of changes in the concentration of pollutants in the semi-arid area,and the correlation between the meteorological elements and the concentration of pollutants,is of great significance for better understanding of the air pollution in semi-arid areas and its prevention and control work.The paper selects the typical sites in the semi-arid region—Saozhong SACOL Station and Shapotou Station as the research object,and uses SACOL Station 2007-2009 and Shapotou Station 2011-2014 observation data to analyze the semi-arid by wavelet analysis and other statistical methods.The characteristics of atmospheric pollutant concentrations in the district were systematically analyzed.Based on this,the influence of meteorological elements on the concentration of pollutants was discussed through correlation analysis,and a multivariate regression prediction model of pollutant concentration based on meteorological elements was established.The characteristics of pollutants,meteorological factors,and weather conditions in the process of typical air pollution in the semi-arid region were further analyzed,and the mechanism of the impact on the pollution process was analyzed.Combined with the WRF-Chem model,the air pollution process of a typical dust event was forecasted.The main conclusions are as follows:?1?The pollutant concentration characteristics analysis results showed that the concentrations of NO,NO2,NOx,SO2 and CO in the semi-arid area all show the characteristics of low summer and high winter,and the O3 concentration shows the characteristics of high summer and low winter,CO2 has no obvious season.With the change characteristics,the peak concentrations of PM10 and PM2.5 all appeared in the spring.From the trend of change,the NO,NO2 and NOx at both sites show a trend of increasing year by year,and O3 shows a trend of decreasing year by year;the SO2 at SACOL station is increasing,and the SO2 at the Shapotou station is Decreased trend;CO,PM10 at the SACOL station showed a decreasing trend,CO2 concentration change was relatively stable,and the concentration of PM2.5.5 at the Shapotou station was relatively stable.The MHAT wavelet analysis found that the concentrations of NO,NO2,NOx,SO2,O3,CO and PM10in the SACOL station were mainly affected by the low-frequency oscillations of the atmosphere,while the CO2 concentration was affected by both the low-frequency oscillation of the atmosphere and the weather process.The concentrations of NO2,SO2,O3,and PM2.5 at Shapotou station are mainly affected by low-frequency oscillations in the atmosphere.NO and NOx are mainly affected by low-frequency oscillations and weather processes in the atmosphere.?2?The correlation analysis showed that at SACOL station the NO is easy to accumulate under the conditions of high humidity and low wind speed;the influenced degree of meteorological factors on NO2 concentration in different seasons are different;In summer,NOx concentration increased significantly under conditions of low temperature,high humidity and calm wind;The correlations between NO,NO2,NOx concentration and temperature are positive in spring and autumn,and negative correlation in summer.Windy weather reduced SO2concentration,and the accumulation of O3 can be easily caused by high-temperature and low-humidity weather.CO pollution is likely to be serious under static wind conditions.CO2concentration is greatly affected by relative humidity and wind direction in spring.The PM10 is not significantly related to meteorological elements and is affected by windy weather only in the spring.At Shapotou station,NO,NO2,NOx and SO2 are all likely to cause the accumulation of pollutants near the surface under conditions of small wind speed.O3 concentrations are likely to be accumulated in high temperature,low humidity,and high wind weather,while the correlation between the variation of PM2.5 concentration and meteorological elements is not obvious.The multiple regression prediction model based on the meteorological factors of pollutant concentration has good prediction effect in the summer and autumn of the SACOL station,but the accuracy rate decreases with the extension of the prediction time.At Shapotou Station,the prediction effect of each season is good,among which the accuracy of autumn is the highest.?3?Analysis of the two typical pollution processes during winter and summer,NO concentration is low at night and high during the day.The concentration of NO2 peaks around3:00 and 12:00 every day.The concentration of SO2 was relatively high during the day.The O3concentration peaks around 4:00 and 16:00 daily.The difference is that the concentration of PM10in summer shows a clear daily variation,while the daily variation in winter is not significant.From the point of view of meteorological elements,relative humidity is relatively high in the early morning,which corresponds to the high concentration of pollutants in the early morning;the wind speed is negatively related to the concentration of pollutants.From the weather situation,when the high-pressure system is affected,the pollutant concentration is relatively high,and when the low-pressure system is affected,the pollutant concentration is relatively low.In winter,the weather is more affected by the weather system,and the hourly changes of the concentration of pollutants in summer are more susceptible to human activities.The model simulation results show that the WRF-Chem model is more feasible for the prediction and prediction of typical dust processes. |
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