Studies On Influence Of The Forest Belt To Intercept And Adsorb Particulate Matter

Particulate matter pollution is a serious air pollution problem. It has a harmful effect on plant, animal and human health no matter the particles come from natural or man-made activities.Three road forest belts in Beijing Olympic forest south park were taken as research object. By setting up six monitoring points in each forest belt, the study chose no-rainy days to monitor the PM concentration monthly and the PM composition quarterly during April to December,2013, and studiedchange laws of particulate matter concentrations and chemical components of PM2.5in forest belts of different width to find out the minimum width of interception and adsorption and establish the effective width model. The findings will provide a reference for follow-up research on forest beltsto cut particles and the belts construction for the purpose of particulate matter interception and adsorption.(1) Comparisons among four particulate matter (TSP, PM10、PM2.5and PM1) concentrations inside and outside the belts have been done. The average concentrations of four sizes outside forest near northern five links are greater than concentrations inside belts and inside the park. And the concentrations of TSP and PM10inside belts are greater than those inside the park. While the concentrations of PM2.5and PM1inside the park are greater than those inside belts. The analysis of chemical compositions of PM2.5inside and outside the forest belts indicates that theaverage concentrations of SO42-and NO3-outside belts near northern five links are the greatest, and the average concentration inside belts are greater than that inside the park. The average concentration of NH4+inside belts is greater than that outside belts near northern five links, and the average concentration inside the park is the smallest. The averageconcentrations of VOC and EC outside belts near northern five links are the greatest, and the average concentrations inside belts are greater than those inside the park. The averageconcentrations inside belts of OC and TC are greater than the concentrations outside belts near northern five links and inside the park, while the concentrations outside forest are greater than the concentrations inside the park.(2) The change particle concentration is different in different seasons and different air quality. Concentrations of four particulate matter change as waveform from the forest belt edge near northern five links to the edge in park. The concentration change laws of TSP are similar to PM10, whilePM2.5and PM1are similar. Coarse particulate matter concentrations across the belts decrease while the fine ones increase. After analyzing concentrations of SO42-, NO3-and NH4+of PM2.5, we find that the change laws of three water soluble ion concentrations are different from season to season. Totally, concentrations of SO42-and NH4+decrease and NO3-increase across the belts. The carbon fractions concentrations of PM2.5are different with different change laws in four seasons. Overall, almost all concentrations of four kinds of carbon fractions of PM2.5decreased across the belts.(3) The forest microclimate is one of the key reasons that results in particulate matter concentrations increase in the belts. There are significant linear correlation between the four particles concentrations and wind direction, wind speed, temperature, relative humidity and atmospheric pressure. The fine particles’absolute values of correlation coefficient aregreater than the coarse particles. That is to say the correlation between the meteorological factors and fine particles is stronger than that of the coarse particles. Relative humidity and wind direction (in angle) are positively correlated with the particulate matter concentrations. While the wind speed, temperature and atmospheric pressure have negative relationship with particle concentrations. And the correlation coefficient absolute value of relative humidity is the greatest. There’s positive correlation between the concentrations of SO42-,NO3-and NH4+and temperature, and the SO42-and NO3-have negative correlation with atmospheric pressure. There isno obvious linear relationship between the three ion concentrations and relative humidity and wind speed. The concentrations of VOC, OC and TC of PM2.5have positive correlation with the atmospheric pressure, and have negative correlation with temperature. EC is negatively related with the atmospheric pressure and wind speed.(4) After the analysis of forest belts’cutting effect on particle concentrations and chemical compositions of captured PM2.5, it points out thatthe effective width to cut particle concentrations of the forest belts is15m to18m in Olympic forestpark south garden, and the effective width tocapture PM2.5chemical compositions is18m to23m. So the effective width to intercept and adsorb particulate matter is18m to23m. The atmospheric pressure, temperature, relative humidityand the concentrations of EC and NO3-have significant correlation with the effective width. And the concentration of EC and atmospheric pressure are positively correlated with the effective width, while the temperature, relative humidity and NO3-concentration are negatively correlated with the width. The study established models of five indexes with the effective width respectively. And the belt’s effective width model is established, too. NO3-concentration of PM2.5(x1) and atmospheric pressure (x2) outside the forest near northern five links were involved in the model. The forest effective width model is Y=-35.66-0.061x1+0.549x2(R2=0.865), and the confidence level is95%.