Alternative techniques to assess road traffic emissions

Today, one of the most important environmental problems in urban areas is air pollution. According to the World Health Organization, air pollution represents a serious risk to human health in many cities of the world. Road traffic is one of the main sources of pollution in cities. Besides, vehicular emissions are released in close proximity to population, increasing the adverse health effects. Road traffic emissions are highly uncertain in developing countries. Existing techniques to assess this source of pollution are expensive and not always accurate. It results difficult for a city from the developing world to afford these techniques and thus, adequate abatement strategies can not be adopted. It is essential to develop methodologies to reduce these uncertainties to manage air quality more effectively. This PhD thesis aims to develop and to implement alternative techniques to assess road traffic emissions. This work focuses on the study of Volatile Organic Compounds (VOCs), this family of pollutants have not been sufficiently studied in cities. The developed techniques were tested during an intensive measuring campaign conducted in Ho Chi Minh City (HCMC), Vietnam. The motorcycles are the main mode of transport in HCMC, this means of transport has contributed to the progress of this rapidly developing city. The high levels of air pollution, the elevated number of motorcycles and especially the limited funding available, made HCMC an interesting place to test the developed methodologies. In a first stage the results of the measuring campaign were used to assess the roadside levels of pollution in HCMC. During the HCMC campaign, 19 C2-C6 VOCs were monitored on-line at roadside level together with other important pollutants. Results show that there is a severe air pollution problem in HCMC. The pollutants that are produced by road traffic are identified by means of a Principal Components Analysis (PCA) receptor Model. The PCA shows that all the VOCs monitored (except isoprene) are produced by motorcycles. It is necessary to develop and to encourage the use of alternative modes of transport in HCMC. The use of the on-line roadside pollutants monitoring together with the PCA showed to be a good first approach to assess the road traffic emissions. This is an affordable technique and it is strongly recommended to use it in cities with limited financial means to study the air pollution problem. This work also presents a new method to estimate road traffic emission factors (EFs). This method is based on a long term tracer experiment conducted during the HCMC campaign. The results of the HCMC tracer experiment were used together with traffic counts and pollutant measurements to calculate the dispersion factors and afterwards the EFs. Estimated EFs for HCMC are within the range of EFs estimated in other studies. Additionally, a Computational Fluid Dynamics Model (CFD) is used to critically evaluate the proposed methodology. The evaluations show that it is possible to accurately estimate the EFs from tracer studies. The methodology proposed here results in an interesting and promising alternative to estimate the EFs. All the techniques presented in this work offer several advantages. Data obtained serve for different purposes at the same time and their use can provide valuable information for urban air quality assessment. For example, concentrations of pollutants are determined at roadside level, as well as their evolution in time, this information is useful for exposure studies. Roadside monitoring can be used to identify the pollutants that are directly emitted by road traffic. Results from the tracer study can be used to estimate the EFs under real urban conditions and to validate dispersion models which in turn can be used in the future to evaluate abatement strategies for such streets.

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