Department of Civil and Environmental Engineering, Rice University, Houston, TX, USA.
J Air Waste Manag Assoc. 2013 Jul;63(7):764-72. doi: 10.1080/10962247.2013.787955.
A year-long study was conducted in Pinal County, AZ, to characterize coarse (2.5 - 10 microm aerodynamic diameter, AD) and fine (< 2.5 microm AD) particulate matter (PMc and PMf, respectively) to further understand spatial and temporal variations in ambient PM concentrations and composition in rural, arid environments. Measurements of PMc and PMf mass, ions, elements, and carbon concentrations at one-in-six day resolution were obtained at three sites within the region. Results from the summer of 2009 and specifically the local monsoon period are presented. The summer monsoon season (July - September) and associated rain and/or high wind events, has historically had the largest number of PM10 NAAQS exceedances within a year. Rain events served to clean the atmosphere, decreasing PMc concentrations resulting in a more uniform spatial gradient among the sites. The monsoon period also is characterized by high wind events, increasing PMc mass concentrations, possibly due to increased local wind-driven soil erosion or transport. Two PM10 NAAQS exceedances at the urban monitoring site were explained by high wind events and can likely be excluded from PM10 compliance calculations as exceptional events. At the more rural Cowtown site, PM10 NAAQS exceedances were more frequent, likely due to the impact from local dust sources. PM mass concentrations at the Cowtown site were typically higher than at the Pinal County Housing and Casa Grande sites. Crustal material was equal to 52-63% of the PMc mass concentration on average. High concentrations of phosphate and organic carbon found at the rural Cowtown were associated with local cattle feeding operations. A relatively high correlation between PMc and PMf (R2 = 0.63) indicated that the lower tail of the coarse particle fraction often impacts the fine particle fraction, increasing the PMf concentrations. Therefore, reductions in PMc sources will likely also reduce PMf concentrations, which also are near the value of the 24-hr PM2.5 NAAQS.
In the desert southwest, summer monsoons are often associated with above average PM10 (< 10 microm AD) mass concentrations. Competing influences of monsoon rain and wind events showed that rain suppresses ambient concentrations while high wind increase them. In this region, the PMc fraction dominates PM10 and crustal sources contribute 52-63% to local PMc mass concentrations on average. Cattle feedlot emissions are also an important source and a unique chemical signature was identified for this source. Observations suggest monsoon wind events alone cannot explain PM10 NAAQS exceedances, thus requiring these values to remain in compliance calculations rather than being removed as exceptional wind events.
在亚利桑那州皮纳尔县进行了一项为期一年的研究，以描述粗颗粒（2.5-10 微米空气动力学直径，AD）和细颗粒（<2.5 微米 AD）颗粒物（分别为 PMc 和 PMf），以进一步了解农村干旱环境中环境 PM 浓度和成分的时空变化。在该地区的三个地点，以每六天一次的分辨率测量了 PMc 和 PMf 质量、离子、元素和碳浓度。介绍了 2009 年夏季，特别是当地季风期的结果。夏季季风季节（7 月至 9 月）及其相关的雨或大风事件，历来是一年内 PM10 NAAQS 超标次数最多的季节。降雨事件使大气得到清洁，降低了 PMc 浓度，从而使各站点之间的空间梯度更加均匀。季风期还以大风事件为特征，增加了 PMc 质量浓度，这可能是由于当地风力引起的土壤侵蚀或运输增加所致。城市监测点的两次 PM10 NAAQS 超标是由大风事件引起的，可以作为特殊事件从 PM10 达标计算中排除。在更为农村化的考特镇站点，PM10 NAAQS 超标更为频繁，这可能是由于当地尘土源的影响。考特镇站点的 PM 质量浓度通常高于皮纳尔县住房和卡萨格兰德站点。地壳物质平均占 PMc 质量浓度的 52-63%。在农村考特镇发现的磷酸盐和有机碳的高浓度与当地的牛饲养作业有关。PMc 和 PMf 之间存在较高的相关性（R2 = 0.63），表明粗颗粒部分的低端通常会影响细颗粒部分，从而增加 PMf 浓度。因此，减少 PMc 源也可能会降低 PMf 浓度，该浓度也接近 24 小时 PM2.5 NAAQS 的值。
在西南部沙漠地区，夏季季风通常与高于平均水平的 PM10（<10 微米 AD）质量浓度有关。季风雨和风事件的相互竞争的影响表明，降雨会抑制环境浓度，而大风则会增加它们。在该地区，PMc 部分占 PM10 的主导地位，地壳源平均占当地 PMc 质量浓度的 52-63%。牛饲养场的排放也是一个重要的来源，并且已经确定了该来源的独特化学特征。观测结果表明，仅季风风事件不能解释 PM10 NAAQS 超标，因此需要将这些值保留在达标计算中，而不是将其作为特殊风事件去除。
