Friedman L, Irsa A P
Science. 1967 Oct 13;158(3798):263-4. doi: 10.1126/science.158.3798.263.
Measurement of the abundance of atmospheric carbon dioxide as an indicator of air pollution has been of very limited value because of variations in urban areas in the substantial concentration of natural carbon dioxide produced from combustion and noncombustion (natural) sources. A solution to this problem is the use of precise isotopic assay of ratios of carbon-13 to carbon-12 in atmospheric carbon dioxide. There is very little variation of carbon isotopic composition in samples taken over rural or urban areas where rapid mixing and diffusion of gaseous combustion products is possible. Significant differences in this composition in samples taken at centrally located points at street level in the lower Manhattan business district show an increase in concentration of atmospheric carbon dioxide of roughly 20 percent produced primarily by automobile exhaust.
将大气中二氧化碳的丰度作为空气污染指标进行测量，其价值一直非常有限，因为城市地区燃烧源和非燃烧（自然）源产生的自然二氧化碳浓度存在很大差异。解决这个问题的方法是对大气二氧化碳中碳-13与碳-12的比例进行精确的同位素分析。在农村或城市地区采集的样本中，由于气态燃烧产物能够快速混合和扩散，碳同位素组成的变化非常小。在曼哈顿下城商业区街道层面的中心位置采集的样本中，这种组成存在显著差异，表明主要由汽车尾气产生的大气二氧化碳浓度增加了约20%。
