There is an excellent Newsletter series published by the International Global Chemistry Project (IGAC). The latest issue has a very important article entitled
“Comparison of Air Pollutant Emissions among Mega-Cities”by Parish et al. The article starts with the paragraph
“The world’s mega-cities represent a wide diversity of cultures and histories, with examples of mega-cities on all of the five major continents. This diversity might be expected to lead to very different patterns of air pollutant emissions. However, as mega-cities develop economically, a convergence of cultures occurs in the sense that automobile fleets and industrial processes develop in similar modes across all cultures. Our goal in this article is to compare and contrast mega-city air pollutant emissions as reflected in measured ambient concentrations of those pollutants.”
Figure 4 in their article shows the major improvement in the concentration of several important pollutants in recent years, as well as the difference among large cities. It viewing this figure, note that the left axis in is units of the logarithm of concentration such that the spread is in units of concentration are, of course, much larger.
The conclusion of the paper has the text
“The speciation of ambient hydrocarbon concentrations in the mega-cities and other U.S. cities examined here (Figures 1-4) reveal a large degree of similarity. This similarity spans the cities in North America and Asia, has remained nearly constant over the past 2 decades in the U.S., and persists over wide ranges of absolute concentrations. A two-part hypothesis most likely explains this similarity: First, on-road vehicle exhaust and the associated evaporative gasoline emissions dominate the ambient hydrocarbon concentrations in all of these urban areas. Second, there is no large difference in the hydrocarbon composition of gasoline between these urban areas.
Comparison of data sets collected in U.S. cities over the past three decades indicate that a substantial decrease in hydrocarbon emissions has occurred even while total vehicle usage has more than doubled. The ambient concentration data suggest that the emission decrease has been larger than indicated by U.S. emission inventories. Thus, U.S. strategies aimed toward controlling hydrocarbon emissions, based upon automobile catalytic converters and minimization of gasoline evaporation, have been quite successful - indeed more successful than indicated by emission inventories.”
This study documents an environmental success story in the United States (from the period 1988-1984 to the period 2005 to 1999) as well as that the United States, despite similarities around the world, has significantly lower atmospheric concentrations at present than found in Mexico City, Tokyo and Beijing. With the introduction of biofuels, there needs to be continued monitoring of a possible rise in these concentrations due to their particular emissions (e.g see
Evidence Of Health Problems With Ethanol Fuels
Will Climate Effects Trump Health Effects In Air Quality Regulations?
Readers of Climate Science are urged to read past and upcoming issues of the IGAC Newsletter for other excellent research contributions, which are expanding our understanding of the climate system.