Sources identification of ammonium in PM2.5 duringmonsoon season in Dhaka, Bangladesh

Ammonia (NH3) is taken up by fine particulate matter (PM2.5), and there are concerns about its impact on the environment and health. The source of NH3, which was thought to be of agricultural sources, has recently been suspected to be non-agricultural sources in urban areas. Here, we collected PM2.5 during the monsoon season in Dhaka, Bangladesh, the most polluted city in the world, and analyzed the delta N-15-NH4+ in PM2.5. As the result, the delta N-15-NH4+ ranged from 9.2% to 34.4%(average: 20.7 +/- 4.8%), the highest of any of the averaged values annual reported in previous researches. In order to performsource analysis, the NH3 concentrations were estimated using the thermodynamic model ISORROPIA-II. The estimated concentration of NH3 gas averaged 40.8 mu g/m(3) (3.0-154.6 mu g/m(3)). The contributions calculated with the mixing model to the delta N-15-NH4+ values in PM2.5 in Dhaka, Bangladesh averaged 25.3 +/- 14 %, 22.8 +/- 10 %, 26.5 +/- 15 %, and 25.4 +/- 10 % for waste, fertilizer, NH3 slip, and fossil fuel combustion, respectively. Non-agricultural sources (NH3 slip, and fossil fuel combustion) accounted for almost half (51.9 %) of the contributions. In addition, the several validation tests of the isotope mixing model were also performed. For validating the uncorrected and corrected source data for delta N-15-NH3, the contribution of non-agricultural sources with uncorrected source data would have been very high (>80 %), much higher than the corrected source data.