Johansson Christer, Norman Michael, Gidhagen Lars
Department of Applied Environmental Science, Stockholm University, S-106 91, Stockholm, Sweden.
Environ Monit Assess. 2007 Apr;127(1-3):477-87. doi: 10.1007/s10661-006-9296-4. Epub 2006 Sep 16.
The size of particles in urban air varies over four orders of magnitude (from 0.001 microm to 10 microm in diameter). In many cities only particle mass concentrations (PM10, i.e. particles <10 microm diameter) is measured. In this paper we analyze how differences in emissions, background concentrations and meteorology affect the temporal and spatial distribution of PM10 and total particle number concentrations (PNC) based on measurements and dispersion modeling in Stockholm, Sweden. PNC at densely trafficked kerbside locations are dominated by ultrafine particles (<0.1 microm diameter) due to vehicle exhaust emissions as verified by high correlation with NOx. But PNC contribute only marginally to PM10, due to the small size of exhaust particles. Instead wear of the road surface is an important factor for the highest PM10 concentrations observed. In Stockholm, road wear increases drastically due to the use of studded tires and traction sand on streets during winter; up to 90% of the locally emitted PM10 may be due to road abrasion. PM10 emissions and concentrations, but not PNC, at kerbside are controlled by road moisture. Annual mean urban background PM10 levels are relatively uniformly distributed over the city, due to the importance of long range transport. For PNC local sources often dominate the concentrations resulting in large temporal and spatial gradients in the concentrations. Despite these differences in the origin of PM10 and PNC, the spatial gradients of annual mean concentrations due to local sources are of equal magnitude due to the common source, namely traffic. Thus, people in different areas experiencing a factor of 2 different annual PM10 exposure due to local sources will also experience a factor of 2 different exposure in terms of PNC. This implies that health impact studies based solely on spatial differences in annual exposure to PM10 may not separate differences in health effects due to ultrafine and coarse particles. On the other hand, health effect assessments based on time series exposure analysis of PM10 and PNC, should be able to observe differences in health effects of ultrafine particles versus coarse particles.
城市空气中颗粒物的大小跨越四个数量级（直径从0.001微米到10微米）。在许多城市，仅测量颗粒物质量浓度（PM10，即直径小于10微米的颗粒物）。在本文中，我们基于瑞典斯德哥尔摩的测量和扩散模型，分析排放、背景浓度和气象条件的差异如何影响PM10和总颗粒物数量浓度（PNC）的时空分布。在交通繁忙的路边位置，PNC主要由超细颗粒物（直径小于0.1微米）构成，这是由于车辆尾气排放所致，与氮氧化物的高度相关性证实了这一点。但由于尾气颗粒物尺寸较小，PNC对PM10的贡献微乎其微。相反，路面磨损是观测到的最高PM10浓度的一个重要因素。在斯德哥尔摩，由于冬季在街道上使用防滑轮胎和牵引沙，路面磨损急剧增加；当地排放的PM10中高达90%可能归因于道路磨损。路边的PM10排放和浓度（而非PNC）受道路湿度控制。由于长距离传输的重要性，城市年平均背景PM10水平在整个城市相对均匀分布。对于PNC，本地源通常主导浓度，导致浓度在时间和空间上有很大梯度。尽管PM10和PNC的来源存在这些差异，但由于共同来源即交通，本地源导致的年平均浓度的空间梯度大小相等。因此，不同地区的人们因本地源导致的年PM10暴露相差2倍，在PNC方面的暴露也会相差2倍。这意味着仅基于年暴露于PM10的空间差异进行的健康影响研究，可能无法区分超细颗粒物和粗颗粒物对健康影响的差异。另一方面，基于PM10和PNC的时间序列暴露分析的健康影响评估，应该能够观察到超细颗粒物与粗颗粒物对健康影响的差异。
