Ultrafine and Submicron Particles in the Urban Environment in Thailand - Size, Concentration, Composition and Health Impacts It is well known that particulate matter (PM) poses a significant health risk, especially to urban dwellers, with often the poorest in society most affected. Ultrafine particles (size smaller than 100 nanometres), as a component of PM, are increasingly implicated in disease and mortality. However, much of the research available in the literature is based on data from the developed world, especially for ultrafine particles, and without robust data it is not possible to determine trends in this important pollutant for Thailand and Bangkok in particular, and strategies for health protection therefore lack this vital information. In addition, aerosol particles provide the single largest source of uncertainty in most global climate models, and production of primary particles and gas precursors e.g. Volatile Organic Compounds (VOCs) from the transport and industrial sectors contribute significantly to this. Therefore, in order for the impact of these activities on climate to be assessed and reduced, determination of sources and levels of emission of both gases and particles much be undertaken. This study will to our knowledge be the first to report ultrafine particle (UFP) number concentration and size distributions in the submicron (smaller than 1 micrometre) size range in urban Bangkok, Thailand. Population in this megacity is expected to rise as urbanisation continues in Thailand, with more people exposed to higher levels of gas and particle pollutants. We will carry out an extensive experimental campaign combining particle concentration, size distribution measurement and sampling with precise laboratory analysis for the particle composition, state-of-the-art atmospheric tracer dispersion experiments and modelling and source apportionment techniques to establish the sources, emission factors, human exposures and inhalation doses for this important health risk. We will undertake work in the three main seasons in Thailand (cool dry, hot dry and rainy) to determine how the climate influences particle size distribution and properties. We will also examine other regional particle source events, such as agricultural fires, visiting rural areas in and out of season for these events to determine their impact on particle concentrations. We aim to provide methodological advances in using non-standard instrumentation for size-segregated airborne particle sampling and for estimation of submicron particle size distributions using cheaper devices than are presently available. By obtaining this new information on typical levels in a variety of microenvironments, in different regions and by identifying sources and emissions factors, direct public health advice on exposure reduction through interventions could be achieved, and first steps taken to engage regulatory bodies and government agencies to aid in their target of reducing particulate pollution to improve the health and quality of life of Thailand and Bangkok residents, and hence reducing the significant current economic cost burden to the Thailand government associated with adverse health impact of particulates. The Newton Fund builds research and innovation partnerships with developing countries across the world to promote the economic development and social welfare of the partner countries.