Department of Chemistry, University of California, Irvine, California 92697, United States.
Department of Environmental Sciences, University of California, Riverside, California 92521, United States.
Environ Sci Technol. 2020 Sep 1;54(17):10524-10532. doi: 10.1021/acs.est.0c02225. Epub 2020 Aug 13.
Total organic carbon (TOC) mass concentrations are decreasing across the contiguous United States (CONUS). We investigate decadal trends in organic carbon (OC) thermal fractions [OC1 (volatilizes at 140 °C), OC2 (280 °C), OC3 (480 °C), OC4 (580 °C)] and pyrolyzed carbon (PC), reported at 121 locations in the nteragency onitoring of tected isual nvironments (IMPROVE) network from 2005 to 2015 for 23 regions across the CONUS. Reductions in PC and OC2 drive decreases in TOC (TOC = OC1 + OC2 + OC3 + OC4 + PC) mass concentrations. OC2 decreases by 40% from 2005 to 2015, and PC decreases by 34%. The largest absolute mass decreases occur in the eastern United States, and relative changes normalized to local concentrations are more uniform across the CONUS. OC is converted to organic mass (OM) using region- and season-specific OM:OC ratios. Simulations with GEOS-Chem reproduce OM trends and suggest that decreases across the CONUS are due to aerosol liquid water (ALW) chemistry. Individual model species, notably aerosol derived from isoprene oxidation products and formed in ALW, correlate significantly ( < 0.05) with OM2, even in arid regions. These findings contribute to literature that suggests air quality rules aimed at SO and NO emissions induce the cobenefit of reducing organic particle mass through ALW chemistry, and these benefits extend beyond the eastern United States.
总有机碳（TOC）质量浓度正在整个美国（CONUS）范围内下降。我们研究了有机碳（OC）热分数[OC1（在 140°C 下挥发）、OC2（280°C）、OC3（480°C）、OC4（580°C）]和热解碳（PC）的十年趋势，这些数据是在美国跨机构监测受保护视觉环境（IMPROVE）网络中 121 个地点，从 2005 年到 2015 年期间，针对 CONUS 23 个地区报告的。PC 和 OC2 的减少导致 TOC（TOC=OC1+OC2+OC3+OC4+PC）质量浓度下降。OC2 从 2005 年到 2015 年下降了 40%，PC 下降了 34%。最大的绝对质量下降发生在美国东部，相对于当地浓度的归一化变化在 CONUS 范围内更为均匀。OC 使用特定于区域和季节的 OM:OC 比转换为有机质量（OM）。使用 GEOS-Chem 进行的模拟再现了 OM 趋势，并表明 CONUS 范围内的下降是由于气溶胶液水（ALW）化学所致。个别模型物种，特别是源自异戊二烯氧化产物并在 ALW 中形成的气溶胶，与 OM2 显著相关（<0.05），即使在干旱地区也是如此。这些发现为文献做出了贡献，这些文献表明，旨在减少 SO 和 NO 排放的空气质量法规通过 ALW 化学引起了减少有机颗粒质量的共同效益，而且这些效益不仅局限于美国东部。
