Lindsay Andrew J, Weesner Brigitte M, Banecker Kyle, Feinman Lee V, Long Russell W, Landis Matthew S, Wood Ezra C
Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104, United States.
US EPA, Office of Research and Development, Research Triangle Park, North Carolina 27711, United States.
ACS EST Air. 2024 Nov 27;1(12):1568-1578. doi: 10.1021/acsestair.4c00138. eCollection 2024 Dec 13.
Gas-phase organic acids are ubiquitous in the atmosphere with mixing ratios of several species, such as formic acid and acetic acid, often as high as several parts per billion by volume (ppbv). Organic acids are produced via photochemical reactions and are also directly emitted from various sources, including combustion, microbial activity, vegetation, soils, and ruminants. We present measurements of gas-phase formic, acetic, propionic, pyruvic, and pentanoic acids from a site near Boise, Idaho, in August 2019 made by iodide-adduct chemical ionization mass spectrometry (CIMS). The site is adjacent to a major interstate highway and beyond the urban/suburban core is surrounded by national forests to the north and northeast and by farmland to the west and south. Maximum mixing ratios of formic, acetic, propionic, and pentanoic acid were typically near 10, 3, 0.4, and 0.2 ppbv, respectively. Observed daytime concentrations of these acids were mostly consistent with other studies, but concentrations were persistently the highest at night between 20:00 to 8:00 (local standard time). Such elevated nighttime concentrations are unlike most other reported organic acid measurements. Although there were times when organic acid concentrations were enhanced by mobile source emissions, the organic acid concentrations appear to be mainly controlled by noncombustion surface primary emissions. Source apportionment by positive matrix factorization (PMF) supports the importance of significant noncombustion, nonphotochemical emissions. Two agricultural surface sources were identified and estimated to contribute to greater than half of total observed concentrations of formic and acetic acid. In contrast to the other measured organic acids, but in agreement with all other reported measurements in the literature, pyruvic acid concentrations peaked during the daytime and were largely controlled by photochemistry.
气相有机酸在大气中普遍存在，甲酸和乙酸等多种有机酸的混合比通常高达十亿分之几（体积分数，ppbv）。有机酸通过光化学反应产生，也直接从各种来源排放，包括燃烧、微生物活动、植被、土壤和反刍动物。我们展示了2019年8月在爱达荷州博伊西附近一个地点，通过碘化物加合物化学电离质谱法（CIMS）对气相甲酸、乙酸、丙酸、丙酮酸和戊酸的测量结果。该地点毗邻一条主要的州际公路，在城市/郊区核心区域之外，北部和东北部被国家森林环绕，西部和南部被农田环绕。甲酸、乙酸、丙酸和戊酸的最大混合比通常分别接近10、3、0.4和0.2 ppbv。这些酸在白天观测到的浓度大多与其他研究一致，但在当地标准时间20:00至8:00之间，夜间浓度一直是最高的。这种夜间浓度升高的情况与大多数其他报道的有机酸测量结果不同。尽管有时有机酸浓度会因移动源排放而增加，但有机酸浓度似乎主要受非燃烧表面一次排放的控制。通过正矩阵因子分解（PMF）进行的源解析支持了显著的非燃烧、非光化学排放的重要性。确定了两个农业表面源，估计它们对观测到的甲酸和乙酸总浓度的贡献超过一半。与其他测量的有机酸不同，但与文献中所有其他报道的测量结果一致，丙酮酸浓度在白天达到峰值，并且在很大程度上受光化学控制。
