GAW Report No. 205 - IGAC Project

CHAPTER 8 – KEY ISSUES AND OUTLOOKresults show that certain synoptic patterns worsen the air quality and induce the UHI. Under thesepatterns, the concentrations of air pollutants increase significantly with the UHI intensity. Theconvergence usually associated with nocturnal UHI causes the accumulation of O 3 precursors, aswell as other air pollutants, thereby worsening the air quality that day and also during the followingdaytime period.The importance of UHI for the impacts of megacities on climate and air quality andtherefore mitigation measures has been well recognized. However, the roles of UHI in the airpollution formation processes and local to regional climate change are not well understood. Morestudies in this area are needed to formulate policies that have co-benefits of air quality and climatechange in megacities.8.7 CONCLUDING COMMENTSThe preceding chapters have described air quality research results from megacities on fiveof the world's continents. Notably, there is wide variability of available information - from LosAngeles, certainly the world's most extensively studied city where research has been ongoing forover six decades, to major megacities where very limited ambient measurements or modellinghave been conducted. This disparity emphasizes the critical need for both intensive fieldcampaigns and routine monitoring throughout the world.Nevertheless, experience in earlier developing megacities (e.g. Los Angeles, Mexico City)provides useful guidance for implementing emission control efforts in any megacity, even beforeextensive measurements and modelling allow formulation of a comprehensive air pollution controlprogramme. Such efforts can yield both immediate and long-term health benefits for the city'spopulation. Initial efforts could include inefficient combustion processes, e.g., open trash burningand cooking or home heating with biofuel and coal. Large industrial facilities and electricalgeneration plants are important emission sources, and a great deal of general knowledge isavailable regarding effective control of their emissions and these facilities can also be early targetsfor air quality improvement. On road motor vehicles are major sources of emissions in all cities,regardless of continent or society, and there is a great deal of similarity between the emissionsfrom vehicle fleets throughout the world. An early introduction of emission controls on newvehicles will sooner begin reducing vehicle emissions through the relatively long process of vehiclefleet turnover.Effective emission control strategies to improve air quality should also take into account theimpact the emission control strategies have on climate. The development of emission controlstrategies should seek "win-win" solutions for air quality problems that simultaneously benefitclimate. Such efforts to optimize the co-benefits of air quality policies for climate will pay dividendsat the local, regional and global scales.ReferencesBench, G., Fallon, S., Schichtel, B., Malm, W., & McDade, C. (2007). Relative contributions offossil and contemporary carbon sources to PM 2.5 aerosols at nine Interagency Monitoringfor Protection of Visual Environments (IMPROVE) network sites. J. Gepophys. Res. -Atmos., 112(D10205), 10. doi: 10.1029/2006JD007708Bettencourt, L. M. A., Lobo, J., Helbing, D., Kühnert, C., & West, G. B. (2007). Growth, innovation,scaling, and the pace of life in cities. Proc. Natl. Acad. Sci. USA., 104(17), 7301-7306. doi:10.1073/pnas.0610172104Blanchard, C. L., Tanenbaum, S., & Lawson, D. R. (2008). Differences between Weekday andWeekend Air Pollutant Levels in Atlanta; Baltimore; Chicago; Dallas–Fort Worth; Denver;Houston; New York; Phoenix; Washington, DC; and Surrounding Areas. J. Air & WasteMange. Assoc., 58(12), 1598-1615. doi: 10.3155/1047-3289.58.12.1598Butler, T. M., & Lawrence, M. G. (2009). The influence of megacities on global atmosphericchemistry: a modelling study. Environ. Chem., 6(3), 219-225. doi: 10.1071/EN08110296