The Holiday Effect Of Air Quality In Xi’an City And The Influence Of Different Control Measures On Air Quality

With the continuous development of society,industrial production has become the main contributor to the rapid economic development,but at the same time,it also brings serious environmental pollution.The increasingly serious atmospheric environment has become one of the factors restricting urban development.Xi’an,as the core city of the national“The Silk Road Economic Belt and the 21st-Century Maritime Silk Road”,plays an important role in the national regional coordinated development strategy.However,the problem of air pollution frequently appears in the public eye.Therefore,it is of great practical significance to analyze the relevant influencing factors of air quality in Xi’an City.This paper takes the air quality of Xi’an city as the research object,analyzes the periodic change of air quality,and explores the effect of special human activities on air quality during“Holidays”.And the extent to which air quality has been improved by the control measures implemented in Xi’an during the COVID-19 epidemic and the current regular implementation of the motor vehicle restriction policy.The main findings are as follows:In the first part of this paper,the change of monthly average pollutant concentration in Xi’an in the past ten years is studied.The results show that:（1）Combined with the periodic change of each pollutant concentration in Xi’an air quality under different time scales,it is found that the change of Xi’an air quality has the main periodic change of 10 months.（2）In recent ten years,the air quality of Xi’an tends to be improved significantly,and SO₂and CO are the most significant;On the time scale of10 months,the air quality of Xi’an showed obvious seasonal characteristics.“Heavy in winter and light in summer”is the seasonal variation rule of pollutant concentration in Xi’an.（3）Through M-K test analysis,it is found that under the background of overall improvement,there are mutation points of all air pollutants in Xi’an during 2017～2018.The second part of this paper evaluates the“Holiday Effect”of air quality in Xi’an.The results showed that:（1）During the short holiday period,the increase of PM_2.5on New Year’s Day was the largest,about 51.2%;The increase of O₃-8h during Tomb-Sweeping Day and Labor Day is 18.53%and 17.98%,respectively.In the absence of special meteorological conditions,the concentration of air pollutants is higher in the short holiday period,and the“Holiday Effect”is more obvious in winter.（2）During the long holiday period,PM_2.5significantly increased by 38.83%and NO₂significantly decreased by about 31.43%during the Spring Festival holiday.During National Day,CO,NO₂and O₃-8h decreased significantly by 20.48%,25.59%and37.66%,and the air quality improved.（3）The hourly concentration change analysis of pollutants during the long-term holiday shows that the large amount of pollutants discharged in the early morning during the Spring Festival leads to poor air quality during the Spring Festival,and the peak value during the National Day is significantly lower than before the National Day.The third part of this paper studies the changes of air quality under different control measures during the COVID-19 outbreak.The results showed that:（1）Due to the influence of epidemic control,the average daily concentrations of PM_2.5,PM₁₀,CO and NO₂in Xi’an during the epidemic control period in 2020 decreased by 17.14%,19.67%,21.99%and 19.82%,respectively,compared with the same period in 2019.（2）Under the intervention of different control measures,the reduction of each pollutant is different:PM₁₀,SO₂and NO₂have the largest decrease in the period of strict control,which is31.95%,18.18%and 55.60%respectively;PM_2.5has the largest decrease in the period of partial control,which is 35.06%;CO has the largest decrease in the period of resumption of work and production,which is about 29.40%,indicating that some pollutants have hysteric effect in the process of policy implementation.（3）During the control period,the correlation between particulate matter and gaseous pollutants is strengthened,and the correlation between O₃and other pollutants changes from negative correlation to positive correlation.（4）Emission reduction estimation of pollutants under different control measures:During the strict control period,the emission reduction concentration estimated by NO₂is the largest,about 45.62%;In some control periods,the emission reduction concentration of PM_2.5is estimated to be the largest,about 68.63%.In the fourth part of this paper,the contribution rate of the previous winter traffic restriction policy and the current normal traffic restriction policy to the improvement of air quality in Xi’an city is discussed.The results show that:（1）The implementation of the winter driving restriction policy in 2016 reduced the concentration of SO₂and O₃-8h,but not significantly,and had a significant increase on PM_2.5,PM₁₀and NO₂.（2）When the normalized driving restriction policy was implemented for the first time in 2018,the concentration of all pollutants showed a rising trend,among which SO₂and NO₂increased significantly.In 2019,the air quality in Xi’an was lower in weekdays than in weekends,so the normal traffic restriction policy had no significant effect on the improvement of air quality.