Milando Chad, Huang Lei, Batterman Stuart
Environmental Health Sciences, University of Michigan, Ann Arbor, MI, USA.
Atmos Environ (1994). 2016 Mar;129:197-209. doi: 10.1016/j.atmosenv.2016.01.012.
PM concentrations throughout much of the U.S. have decreased over the last 15 years, but emissions and concentration trends can vary by location and source type. Such trends should be understood to inform air quality management and policies. This work examines trends in emissions, concentrations and source apportionments in two large Midwest U.S. cities, Detroit, Michigan, and Chicago, Illinois. Annual and seasonal trends were investigated using National Emission Inventory (NEI) data for 2002 to 2011, speciated ambient PM data from 2001 to 2014, apportionments from positive matrix factorization (PMF) receptor modeling, and quantile regression. Over the study period, county-wide data suggest emissions from point sources decreased (Detroit) or held constant (Chicago), while emissions from on-road mobile sources were constant (Detroit) or increased (Chicago), however changes in methodology limit the interpretation of inventory trends. Ambient concentration data also suggest source and apportionment trends, e.g., annual median concentrations of PM in the two cities declined by 3.2 to 3.6 %/yr (faster than national trends), and sulfate concentrations (due to coal-fired facilities and other point source emissions) declined even faster; in contrast, organic and elemental carbon (tracers of gasoline and diesel vehicle exhaust) declined more slowly or held constant. The PMF models identified nine sources in Detroit and eight in Chicago, the most important being secondary sulfate, secondary nitrate and vehicle emissions. A minor crustal dust source, metals sources, and a biomass source also were present in both cities. These apportionments showed that the median relative contributions from secondary sulfate sources decreased by 4.2 to 5.5% per year in Detroit and Chicago, while contributions from metals sources, biomass sources, and vehicles increased from 1.3 to 9.2% per year. This first application of quantile regression to trend analyses of speciated PM data reveals that source contributions to PM varied as PM concentrations decreased, and that the fraction of PM due to emissions from vehicles and other local emissions has increased. Each data source has uncertainties, but emissions, monitoring and PMF data provide complementary information that can help to discern trends and identify contributing sources. Study results emphasize the need to target specific sources in policies and regulations aimed at decreasing PM concentrations in urban areas.
在过去15年里，美国大部分地区的细颗粒物（PM）浓度有所下降，但排放和浓度趋势会因地点和源类型而异。应了解这些趋势，以为空气质量管理和政策提供信息。这项工作研究了美国中西部两个大城市——密歇根州底特律市和伊利诺伊州芝加哥市——的排放、浓度和源分配趋势。利用2002年至2011年的国家排放清单（NEI）数据、2001年至2014年的特定环境PM数据、正矩阵因子分解（PMF）受体模型的分配结果以及分位数回归，对年度和季节趋势进行了调查。在研究期间，全县范围的数据表明，点源排放减少（底特律）或保持不变（芝加哥），而道路移动源排放保持不变（底特律）或增加（芝加哥），然而方法的变化限制了对排放清单趋势的解读。环境浓度数据也表明了源和分配趋势，例如，两个城市中PM的年度中位数浓度每年下降3.2%至3.6%（快于全国趋势），硫酸盐浓度（由于燃煤设施和其他点源排放）下降得更快；相比之下，有机碳和元素碳（汽油和柴油车辆尾气的示踪剂）下降得更慢或保持不变。PMF模型在底特律识别出9个源，在芝加哥识别出8个源，其中最重要的是二次硫酸盐、二次硝酸盐和车辆排放。两个城市中还存在一个较小的地壳尘源、金属源和生物质源。这些分配结果表明，底特律和芝加哥二次硫酸盐源的中位数相对贡献每年下降4.2%至5.5%，而金属源、生物质源和车辆的贡献每年从1.3%增加到9.2%。分位数回归首次应用于特定PM数据的趋势分析，结果表明，随着PM浓度下降，源对PM的贡献各不相同，并且车辆和其他本地排放产生的PM所占比例有所增加。每个数据源都存在不确定性，但排放、监测和PMF数据提供了互补信息，有助于辨别趋势并确定贡献源。研究结果强调，在旨在降低城市地区PM浓度的政策和法规中，有必要针对特定源采取措施。
