CASE STUDY Measurement of Ambient NH 3 , NO and NO 2 at an Urban Area of Kolkata, India S. K. Sharma 1 *, Rohtash 1 , T. K. Mandal 1 , N. C. Deb 2 and S. Pal 2 1 Radio and Atmospheric Sciences Division, CSIR-National Physical Laboratory, Dr. K S Krishnan Road, New Delhi 110 012, India 2 ECSU, Indian Statistical Institute, Barrackpore Trunk Road, Kolkata 700 108, India Received: 12 May 2015 / Accepted: 30 July 2015 Ó Metrology Society of India 2015 Abstract: Mixing ratios of ambient NH 3 , NO and NO 2 were measured in campaign mode at Kolkata a megacity of Indo- Gangetic plain of India to study the diurnal variation and mixing ratios of NH 3 , NO and NO 2 during 24–27 February 2012. The present study has been carried out on campaign based measurement of mixing ratios of NH 3 , NO and NO 2 for short period of time at Kolkata represent the indicative values over the region. The average mixing ratios of ambient NH 3 , NO and NO 2 were recorded as 43.4 ± 7.0 ppb, 46.0 ± 8.7 ppb and 31.9 ± 5.5 ppb at Kolkata. In the present case, significant diurnal variation of NH 3 , NO and NO 2 were recorded at Kolkata during study. Mixing ratio of ambient NH 3 reaches its maxima (78.9 ppb) at night and minimum during daytime. Result reveals that the ambient NH 3 mixing ratio is positively correlated with ambient NO (r 2 = 0.395) and NO 2 (r 2 = 0.404) mixing ratio and significant negatively correlated with ambient temperature (r 2 = –0.669). Surface wind direction and wind speed analysis indicates that the local acitivities (livestock, drainage, agriculture, vehicles etc.,) may be the possible sources of ambient NH 3 at the observational site of Kolkata. Keywords: Ambient NH 3 ; NO; NO 2 ; Chemiluminescence method 1. Introduction Over the past few decades, human activities leading to the production of reactive nitrogen (NH 3 , NO x , HNO 3 ,N 2 O, and N 2 O 5 , HONO, PAN, NH 4 ? , NO 3 – , urea, amines, amino acids and proteins etc.,) from N 2 have exceeded the natural rate of nitrogen fixation on land at the global scale [1]. Although nitrogen is a major nutrient that governs growth and reproduction of organisms, accumulations of reactive nitrogen from various sources have a profound effect on air and water quality [2, 3]. Ambient NH 3 (one of the reactive nitogen) is now considered as one of the primary air pol- lutants, influencing acidic deposition along with nitrogen oxides (NO x ) and sulphur dioxide (SO 2 ). Following the deposition, it plays a major role in the biogeochemical process of sensitive ecosystems like forest, river, coastal and soil. NH 3 can immediately react with atmospheric acids (H 2 SO 4 or HNO 3 or HCl) to form secondary atmospheric particulates like (NH 4 ) 2 SO 4 , NH 4 NO 3 and NH 4 Cl etc., [3, 4] or deposit onto the Earth’s surface. The importance of NH 3 in urban areas is related to its role as a precursor for secondary aerosol [5, 6]. These NH 4 ? aerosols contribute significantly to fine particle and have implication on human health. Based on its ability to form fine particles of NH 4 ? [(NH 4 ) 2 SO 4 , NH 4 NO 3 , NH 4 Cl] atmospheric NH 3 plays a major role in global radiative forcing [7]. Atmospheric NH 3 (lifetime *-5 days) may be transported over 10 to 100 km from the source depending on the meteorological conditions; however, NH 4 ? (lifetime *1–15 days) may be transported to much longer distance (100 to [ 1000 km) [8, 9]. Consequently, atmospheric NH 3 contributes to international transbound- ary air pollution issues on long range transboundary pol- lution [10]. These NH 4 ? aerosols contribute significantly to the fine particle formation (size \ 2.5 lm) and have implications for human health [11]. They limit atmospheric visibility and alter global radiation budgets [12]. The most recent consideration for NH 3 emissions on the global scale is linked to climate change based on its ability to form *Corresponding author, E-mail: sudhir@nplindia.org M  APAN-Journal of Metrology Society of India DOI 10.1007/s12647-015-0147-z 123