Influence of extensive compressed natural gas (CNG) usage on air quality Jeeranut Suthawaree a, * , Helena Akhter Sikder a, 1 , Charlotte Emily Jones a,1 , Shungo Kato a,1 , Hitoshi Kunimi a,1 , Abu Naser Mohammed Hamidul Kabir b, 2 , Yoshizumi Kajii a,1 a Faculty of Urban and Environmental Science, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji-city, Tokyo, 192-0397, Japan b Department of Applied Chemistry and Chemical Engineering, Faculty of Engineering and Technology, University of Dhaka, Curzon Hall Area, Dhaka, 1000, Bangladesh article info Article history: Received 25 October 2011 Received in revised form 24 January 2012 Accepted 25 January 2012 Keywords: Compressed natural gas Air quality Dhaka city Bangladesh Ozone formation potential abstract Compressed Natural Gas (CNG) is an inexpensive, indigenous energy resource which currently accounts for the majority of automobile and domestic energy consumption in Bangladesh. This extensive CNG usage, particularly within the capital city, Dhaka, heavily influences the atmospheric composition (and hence air quality), yet to date measurements of trace gases in regions dominated by CNG emissions are relatively limited. Here we report continuous observations of the atmospherically important trace gases O 3 , CO, SO 2 , NO x and volatile organic compounds (VOC), in ambient air in Dhaka City, Bangladesh, during May 2011. The average mixing ratios of O 3 , CO, SO 2 , and NO x for the measurement period were 18.9, 520.9, 7.6 and 21.5 ppbv, respectively. The ratios of CO to NO reveal that emissions from gasoline and CNG-fuelled vehicles were dominant during the daytime (slope of w26), while in contrast, owing to restrictions imposed on diesel fuelled vehicles entering Dhaka City, emissions from these vehicles only became significant during the night (slope of w10). The total VOC mixing ratio in Dhaka was w5e10 times higher than the levels reported in more developed Asian cities such as Tokyo and Bangkok, which consequently gives rise to a higher ozone formation potential (OFP). However, the most abundant VOC in Dhaka were the relatively long-lived ethane and propane (with mean mixing ratios of w115 and w30 ppbv, respectively), and as a consequence, the ozone formation potential per ppb carbon (ppbC) was lower in Dhaka than in Tokyo and Bangkok. Thus the atmospheric composition of air influenced by extensive CNG combustion may be characterized by high VOC mixing ratios, yet mixing ratios of the photochemical pollutant ozone do not drastically exceed the levels typical of Asian cities with considerably lower VOC levels. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction In 2010 it was estimated that more than 51% of world’s population reside in urban areas, and this is projected to increase to 61% by the year 2030 (United Nations, 2009). Owing to this rapid growth in the urban population, the issue of urban environmental pollution now requires urgent attention, with particular emphasis on identifying major sources of pollutants and developing measures to lead towards an integrated and sustainable solution. Dhaka, the capital of Bangladesh, is one of the most densely populated cities in the world (Dhaka metropolitan area; population of 14.65 million residing within an area of 1353 km 2 ) and has been suffering from diverse environmental issues including wastewater discharge, solid waste management, noise pollution, and air quality [Regional Resource Centre for Asia and the Pacific (RRCAP), 2005]. With regard to air pollution, Bangladesh was estimated to emit the second largest amount of carbon monoxide (CO), and the third largest amounts of nitrogen oxides (NO x ) and non-methane volatile organic compounds (NMVOC) of all South Asian countries [Emission Database for Global Atmospheric Research (EDGAR), 2011]. Gurjar et al. (2008) reported that Dhaka is the city with the poorest air quality among other 18 megacities according to its multi-pollutant index (MPI), which is calculated based on the levels of three air pollutants e total suspended particles (TSP), sulphur dioxide (SO 2 ), and nitrogen dioxide (NO 2 ). Bangladesh’s air pollution issues have recently come to international attention, as the transport of air pollution outflow westward from Bangladesh towards Europe was demonstrated by model simulations of a southern Asian CO tracer (Lawrence and Lelieveld, 2010). As such, air quality in Bangladesh should be regarded as more than simply a local scale issue, and is potentially a cause for concern for numerous countries in West Asia and Eastern Europe. The brick making industry is notoriously deemed as the largest stationary source of air pollutants in Bangladesh. The alarming maximum CO and total hydrocarbon mixing ratios observed from * Corresponding author. Tel.: þ81 42 677 2833; fax: þ81 42 677 2837. E-mail address: deutschf@gmail.com (J. Suthawaree). 1 Tel.: þ81 42 677 2833; fax: þ81 42 677 2837. 2 Tel.: þ880 2 9661920 73x7364. Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2012.01.066 Atmospheric Environment 54 (2012) 296e307