Abundance and distribution of gaseous ammonia and particulate ammonium at Delhi, India

Abstract. This study reports abundance and distribution of gaseous NH₃ and particulate NH₄⁺ at Delhi. Gaseous NH₃ and particulate NH₄⁺ concentrations were measured during pre-monsoon, monsoon and post-monsoon seasons of the years 2010 and 2011. Average concentrations of gaseous NH₃ during pre-monsoon, monsoon and post-monsoon seasons were recorded as 26.4, 33.2 and 32.5 μg m⁻³, respectively. Gaseous NH₃ concentrations were the highest during monsoon, thought to be due to decay and decomposition of plants and other biogenic material under wet conditions, leading to increased NH₃ emission. The results showed that particulate NH₄⁺ was always lower than the gaseous NH₃ during all the seasons. The concentrations of particulate NH₄⁺ were recorded as 11.6, 22.9 and 8.5 μg m⁻³ during pre-monsoon, monsoon and post-monsoon seasons, respectively. The percent fraction of particulate NH₄⁺ was noticed to be highest during the monsoon season, which is attributed to increased humidity levels favouring partitioning into the aerosol phase. On an average, 33.3% of total N-NH_x was present as particulate NH₄⁺. Higher concentrations of NH₃ noticed during night time may be due to stable atmospheric conditions. The study highlighted that, as compared with rural sites, urban sites showed higher concentrations of gaseous NH₃ in India, which may be due to higher population density, human activities and poor sanitation arrangements.