However, the same homogeneity is not seen in several large fast-growing cities in East Asia, where high wet deposition rates match high, unregulated emissions.
"This is the same thing that transpired in the United States in the period leading up to the 1970s," Rao said. "We had rapid urban growth, rising emissions and rising wet deposition, which is analogous to what's happening now in places like Beijing and New Delhi."
For example, the concentration of nitrate and sulfate in rainwater in the Chinese city of Xi'an is 10 times greater than in New York City.
The reduction in wet deposition in U.S. cities is especially significant considering that the time period also was marked by dramatic growth in gross domestic product, urban population and the number of vehicles.
"This is encouraging," Gall said. "When mitigation strategies are widely adapted, it is possible for cost-effective engineering solutions to protect the environment while simultaneously allowing people to maintain the same quality of life."
The researchers have developed a model that can be used to simulate and predict how wet deposition rates vary across megacities located in diverse climatic regions, such as arid or humid.
"Given certain emissions and rainfall patterns, we can now project how wet deposition rates would increase initially and then decrease when and if regulations are in place," Rao said. "Additionally, the model can be used to examine wet deposition rates under climate-change scenarios."
The study findings also have implications for variations in wet deposition rates under shifting weather resulting from climate-change scenarios, as well as rapid urbanization in emerging economies.
Although annual wet deposition patterns are influenced by variability in rainfall amounts both within a year and from year to year, the effects are much greater when pollutant-emission regulation is weak. For example, even though Xi'an, Ch
|Contact: Emil Venere|