Atmospheric Particulate Concentration Change In Urban Forest Area

Atmospheric particulate pollution of cities in arid regions has become a common phenomenon.Inhalable particulate matter(PM₁₀),fine particulate matter(PM_2.5),and ultrafine particulate matter(PM_1.0)have received increasing attention.High concentrations of atmospheric particulates in haze weather not only affect people’s travel,but also cause serious harm to people’s health.Urban forest is an important part of the urban ecosystem.It can reduce the concentration of atmospheric particulate matter in a variety of ways,and has a strong reduction effect on atmospheric particulate matter,which is conducive to the improvement of urban ambient air quality.Yanerwo Ecological Forest in Urumqi is the research area in this study.The atmospheric particulate matter(PM_1.0,PM_2.5 and PM₁₀)concentrations and environmental factors such as temperature,relative humidity and wind speed are monitored synchronously from August 2018 to July 2019.The temporal and spatial distribution of atmospheric particulate matter of various particle sizes and their response to meteorological factors are analyzed.The influence of weather conditions on the concentration of particulate matter regulated by forests and ability to reduce atmospheric particulate matter in urban forests with different configurations of green space structures are discussed.The findings are as follows:（1）The daily variety trend of PM₁₀,PM_2.5,and PM_1.0 concentrations showed an approximately“V”shape,with high values at 8:00 in the morning and 18:00 in the evening,and low values at 14:00 at noon;the concentration of PM₁₀ within a day variety range is the largest,which were followed by PM_2.5 and PM_1.0 concentration performing relatively gently;the particulate matter concentration at the roadside monitoring points outside the forest is significantly higher than the three monitoring points in the forest,and the trend of seasonal variation of particulate matter concentration is:winter>Autumn>Spring>Summer;the changes of three kinds of particulate matter from roadside to the inside of the ecological forest all showed waveform shape.The trends of the particle concentration changes in spring and winter are similar,and the particle concentrations in the forest monitoring point near the roadside are the lowest.The change trend of particulate matter concentration in summer and autumn was similar,and the particulate matter concentration was the lowest at the monitoring point of the forest land center.（2）The abilities of different configuration modes for green space structures are significant differences to reduce particulate matter in different time periods.In summer,the reduction rates of 4 different green space structures on the concentration of 3 different particle sizes were the largest,followed by autumn and spring.In winter,the reduction rates of the green space structure on the particle concentration were the smallest.comprehensively throughout the year,the average reduction rate of atmospheric particulate matter with different particle sizes for different types of vegetation patterns in the green land is expressed as"arbor-bush-grass">"arbor-bush">"arbor-grass">"grassland",indicating"arbor-bush-grass"structure has a strong ability to reduce particles with different particle sizes.（3）Meteorological factors have a greater impact on atmospheric particulate matter.The relative humidity has a positive correlation with the concentration of the three kinds of particulate matter,and the atmospheric temperature and wind speed have a negative correlation with the concentration of the three kinds of particulate matter.The absolute value of the correlation coefficient is expressed as atmospheric temperature>relative humidity>wind speed;the wind speed and temperature in the forest land are smaller than the surrounding area and humidity is greater than the surrounding area;the occurrence of microclimate in the forest is an important reason for the increase in particulate matter concentration in the forest.（4）Rainfall weather has a significant effect on the concentration of atmospheric particulate matter.Under 7 kinds of weather conditions before and after rainy days,the daily mean value of atmospheric particulate matter concentration shows a trend of cloudy and overcast weather>cloudy weather>sunny weather>overcast weather after rains>cloudy weather after rains>sunny days after rains>rainy days.The particulate matter concentration gradually increased three days before the rain,reached a relatively high value on the day before the rain,and quickly decreased to a relatively low value on the day of the rain,after which the particulate matter concentration gradually rose again.（5）In mild haze weather,the concentration of particulate matter with different particle diameters in the ecological forest is slightly higher than that outside the ecological forest.In the morning,the concentration of particulate matter is higher.As the haze dissipates in the afternoon,the weather conditions are improved and the particulate matter concentration begins to decrease.After that,the particulate matter concentration was at a low level from 14:00 to 17:00.