Effect of windbreaks on particle concentrations from agricultural fields under a variety of wind conditions in the farming-pastoral ecotone of northern China

摘要

Wind erosion from agricultural fields contributes substantial amounts of particulate matter (PM) in the form of dust to the atmosphere, with significant impacts on air quality and human health. Vegetation barriers affect particle transport via altering air flow, yet the impact of windbreaks on PM concentrations from agricultural soil erosion is still unknown. This study describes brief campaigns to explore the effects of windbreaks on PM concentrations in Zhangbei County, Heibei Province, China. Measurements were made in arable lands with windbreaks, of which the dominant tree species was Populus, following dust events from April to May, when the trees were without leaves. We selected windbreaks with different structures and measured PM concentrations at the windward and the leeward sides of the windbreaks, using high time-resolution measurements. The effects of windbreaks were quantified by calculating the PM concentration ratios in front of and behind the windbreaks. During dust events, the average value of maximum PM10 emissions was 109.87 mu g/m(3), which was above the threshold established by the World Health Organization (WHO) for air quality. The PM10 emissions increased with air temperature and wind speed. The highest PM10 emission was observed at a relative air humidity of 20%. PM1 and PM2.5 concentrations were not lower behind the windbreak than in front of the windbreak in most of the events, while PM10 concentrations could be reduced by an average of 27%. A significant increase in PM2.5/PM10 by 56.86% behind the windbreak indicates the high efficiency of the windbreak to reduce PM10 levels. Simply planting trees can, in some cases, increase downwind PM concentrations. Vegetation configuration and avoiding locating residential areas in the immediate lee of windbreaks should be considered when planning windbreaks.