Formaldehyde (HCHO) is generated from direct urban emission sources and secondary production from the photochemical reactions of urban smog. HCHO is linked to tropospheric ozone formation, and contributes to the photochemical reactions of other components of urban smog. In this study, pollution plume intercepts during the Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) campaign were used to investigate and characterize the formation of HCHO in relation to several anthropogenic tracers. Analysis of aircraft intercepts combined with detailed chemical box modeling downwind of several cities suggests that the most important contribution to observed HCHO was primary emission. A box model analysis of a single plume suggested that secondary sources contribute to 21 ± 10% of the observed HCHO. Ratios of HCHO/CO observed in the northeast US, from Ohio to New York, ranging from 0.2% to 0.6%, are consistent with direct emissions combined with at most modest photochemical production. Analysis of the nocturnal boundary layer and residual layer from repeated vertical profiling over urban influenced areas indicate a direct HCHO emission flux of 1.3 × 10¹⁴ molecules cm⁻² h⁻¹. In a case study in Atlanta, GA, nighttime HCHO exhibited a ratio to CO (0.6%–1.8%) and was anti‐correlated with O₃. Observations were consistent with mixing between direct HCHO emissions in urban air masses with those influenced by more rapid HCHO photochemical production. The HCHO/CO emissions ratios determined from the measured data are 2.3–15 times greater than the NEI 2017 emissions database. The largest observed HCHO/CO was 1.7%–1.8%, located near co‐generating power stations.

中文翻译：

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冬季甲醛：美国东部的空气传播观测和污染源分配

甲醛（HCHO）由直接的城市排放源产生，而副产物则由城市烟雾的光化学反应产生。HCHO与对流层臭氧的形成有关，并有助于城市烟雾中其他成分的光化学反应。在这项研究中，冬季运输，排放和反应性调查（WINTER）活动中的污染物羽流截距用于调查和表征与几种人为示踪剂有关的HCHO的形成。对飞机拦截的分析以及顺风顺水的几个城市的详细化学箱模拟表明，对观测到的HCHO的最重要贡献是主要排放。对单个羽流进行的箱型模型分析表明，次要来源占观察到的HCHO的21±10％。在美国东北部（从俄亥俄州到纽约）观察到的HCHO / CO比率在0.2％至0.6％的范围内，与直接排放和最多适度的光化学生产相一致。通过对城市受灾地区重复进行垂直剖面分析得出夜间边界层和残留层，表明直接HCHO排放通量为1.3×10^14个分子cm ^-2 h ^-1。在佐治亚州亚特兰大的一个案例研究中，夜间HCHO与CO的比率（0.6％–1.8％）且与O ₃反相关。观察结果与城市空气中直接HCHO排放与受更快速的HCHO光化学生产影响的排放之间的混合是一致的。根据实测数据确定的HCHO / CO排放比是NEI 2017排放数据库的2.3–15倍。观测到的最大HCHO / CO为1.7％–1.8％，位于热电联产电站附近。