Organic species within atmospheric particles vary widely in molecular structure. The variety of molecules that comprise the aerosol make it rich in information about its sources and chemical life cycle but also make particulate organic matter (OM) difficult to characterize and quantify. In Part 1 of this pair of papers, we described a direct method for measuring the composition and concentrations of OM in aerosol samples that is compatible with routine monitoring of air quality. This method uses Fourier transform infrared (FT-IR) spectrometry of filter-based aerosol samples to quantify bonds, or functional groups, that represent the majority of organic composition. Summation of these functional groups gives OM. In this paper, functional group and OM concentrations are directly measured in 8 years of aerosol samples collected at two rural and two urban sites in the Southeastern Aerosol Research and Characterization (SEARCH) network. FT-IR spectrometry with a multivariate calibration is used to quantify the concentrations of aliphatic C−H (aCH), carboxylic acid (COOH), oxalate (oxOCO; representing carboxylates), non-acid and non-oxalate carbonyl (naCO), and alcohol O−H (aCOH) in approximately 3500 filter samples collected every third day from 2009 through 2016. In addition, measurements are made on samples from all days in 2016. To the best of our knowledge, this is the longest time period over which this type of analysis has been applied, and this work also demonstrates the application of a more chemically complete and less destructive method than in prior work using alternate techniques. A decline in the total OM is observed from 2011 to 2016 due to a decrease in the more oxygenated functional groups (carboxylic acid and oxalate) and is attributed to anthropogenic SO₂ and/or volatile organic compound (VOC) emissions reductions. The trend in OM composition is consistent with those observed using more time- and labor-intensive analytical techniques. Concurrently, the fractional contributions of aCOH and naCO to OM increased, which might be linked to monoterpene-derived secondary OM, with plausible influences from decreasing NO_x and/or increasing O₃ concentrations. In addition, this work demonstrates that OM to organic carbon ($\mathrm{OM}/\mathrm{OC}$) ratios in the southeastern US (SE US) did not appreciably change over the study time period as a result of these competing functional group contributions to OM. Monthly observations support the sources suggested by these overall trends, including evidence of strong biogenic and photo-oxidation influences. Daily samples from 2016 further elucidate the consistent impact of meteorology and biomass burning events on shorter-term OM variability, including prescribed burning in the winter or spring and wildfires in the autumn, although these sources did not appear to be strong contributors to long-term OM or composition trends in the SE US. These shorter-term and spatial observations reinforce the results of the broader dataset and serve to evaluate the applicability of FT-IR spectrometry measurement to trends analysis on various timescales relevant to routine monitoring of aerosol composition.

中文翻译：

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量化美国东南部颗粒物过滤器样品中的有机物和官能团——第 2 部分：时空趋势

大气颗粒中的有机物种在分子结构上差异很大。构成气溶胶的分子种类繁多，使其拥有丰富的有关其来源和化学生命周期的信息，但也使颗粒有机物 (OM) 难以表征和量化。在这对论文的第 1 部分中，我们描述了一种用于测量气溶胶样品中 OM 的成分和浓度的直接方法，该方法与空气质量的常规监测兼容。该方法使用基于过滤器的气溶胶样品的傅里叶变换红外 (FT-IR) 光谱法来量化代表大部分有机成分的键或官能团。这些官能团的总和得到 OM。在本文中，在东南气溶胶研究和表征 (SEARCH) 网络的两个农村和两个城市地点收集的 8 年气溶胶样本中直接测量了官能团和 OM 浓度。具有多变量校准的 FT-IR 光谱法用于量化脂肪族化合物的浓度C-H（ACH），羧酸（COOH），草酸盐（oxOCO ;代表羧酸盐），非酸和非草酸盐羰基（NACO），和醇O - H在大约3500过滤器样品（AcOH中）收集每三天从 2009 年到 2016 年。此外，对 2016 年所有日子的样本进行了测量。据我们所知，这是应用此类分析的最长时间段，这项工作也证明了应用与使用替代技术的先前工作相比，化学上更完整且破坏性更小的方法。从 2011 年到 2016 年，观察到的总有机质下降是由于更多含氧官能团（羧酸和草酸盐）的减少，这归因于人为SO ₂和/或挥发性有机化合物 (VOC) 排放减少。OM 组成的趋势与使用更多时间和劳动密集型分析技术观察到的趋势一致。同时，aCOH 和 naCO 对 OM 的部分贡献增加，这可能与单萜衍生的次级 OM 有关，可能会受到降低NO _x和/或增加O ₃浓度的影响。此外，这项工作表明 OM 对有机碳（$\mathrm{OM}/\mathrm{超频}$) 美国东南部 (SE US) 的比率在研究时间段内没有明显变化，因为这些竞争性功能组对 OM 的贡献。每月的观察结果支持这些总体趋势所暗示的来源，包括强烈的生物和光氧化影响的证据。2016 年的每日样本进一步阐明了气象学和生物量燃烧事件对短期 OM 变异性的持续影响，包括规定的冬季或春季燃烧和野火秋季，尽管这些来源似乎并不是美国东南部长期 OM 或成分趋势的有力贡献者。这些短期和空间观察强化了更广泛数据集的结果，并有助于评估 FT-IR 光谱测量对与气溶胶成分常规监测相关的各种时间尺度的趋势分析的适用性。