GAW Report No. 205 - IGAC Project

CHAPTER 3 - ASIAthe negative health effects resulting from exposure to the rise in pollutants. The role of the transportsector on ambient levels of particulates is considered by Halek et al. [2004] where the agedistribution and polluting potential of the car fleet is examined in conjunction with seasonal variationin PM levels.SO 2 trends between 1995 and 2002 were the focus of a study by Aspari et al. [2002].Measurements were taken from seven main monitoring stations at different locations in the city. Thetrend in annual concentrations was downward until 1998, but since then there has been anincreasing trend. The seasonality of concentrations is similar to the previous studies.Information on spatial and temporal concentrations of volatile organic compounds (VOC) ishard to find. Jafari and Ebrahimi [2007] provide information on measured concentrations forBenzene. Finding that that benzene concentrations in Tehran average around 0.1 mg/m 3 , they notethat this is significantly higher than the U.S. Environmental Protection Agency (EPA)recommendation.Relationships of the trends to regulationsIn 1995, Tehran Municipality initiated a two-year project entitled ‘Tehran TransportEmissions Reduction Project’ to identify strategies for reducing motor vehicle emissions, and also toconsider greenhouse gas emissions. The Global Environmental Facility (GEF) and the localmunicipality supported this research. Key recommendations from this programme included phasingout older more polluting vehicles, cleaner fuel, mandatory inspection and maintenance, publiceducation and better traffic management. However, lack of coordination between local authoritieshas meant that the key recommendations have not been successfully implemented(Asadollah-Fardi) despite the Clean Air Act passed by the Iranian Parliament in 1995 to address thisimportant issue. This act prohibits the use of polluting (smoking) vehicles in urban areas, amongstother decrees.A cursory examination of annual averages from a monitoring station in the commercialheartland of Tehran (Bazaar) shows a decreasing trend for all pollutants (Asadollah-Fardi,Unpublished Report), but a more robust assessment is needed. Future studies should considerstatistically removing the influence of inter-annual variation in meteorology.Climatic change issuesA clear link between global climate change and air quality has not been established forTehran, however a summary of findings up to now follows next. Significant, increasing trends havebeen found in the annual statistics for temperature (Figure 63). Several climactic metrics, includingmaximum of daily maximum and minimum temperature, the annual minimum of daily maximum andminimum temperature, the number of summer nights, and the number of days where dailytemperature has exceeded its 90th percentile were examined by Zhang el al. [2005]. Analysis ofdaily airport data from 1956 to 2003 has shown significant negative trend in frost days and asignificant positive trend for summer days when maximum temperature exceeds 25 °C. Significantnegative trends have been found in the number of days when daily temperature is below its 10thpercentile. Positive trend in extreme precipitation events for Tehran was also found by Asgari et al.[2008].Figure 63 - Trends in mean annual temperature and population for Tehran130