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Role of atmospheric ammonia in the formation of inorganic secondary particulate matter: A study at Kanpur,India

Authors:	Mukesh Sharma Shyam Kishore S N Tripathi S N Behera

Institution:	(1) Department of Civil Engineering, Indian Institute of Technology, Kanpur, 208016, India

Abstract:	Levels of fine Particulate Matter (PM_fine), SO₂ and NO_x are interlinked through atmospheric reactions to a large extent. NO_x, NH₃, SO₂, temperature and humidity are the important atmospheric constituents/conditions governing formation of fine particulate sulfates and nitrates. To understand the formation of inorganic secondary particles (nitrates and sulfates) in the atmosphere, a study was undertaken in Kanpur, India. Specifically, the study was designed to measure the atmospheric levels of ${\text{NH}}^{{\text{ + }}}_{{\text{4}}} ,{\text{Ca}}^{{{\text{2 + }}}} ,{\text{Mg}}^{{2 + }} ,{\text{Na}}^{{\text{ + }}} ,{\text{K}}^{{\text{ + }}} ,{\text{NO}}^{{\text{ - }}}_{{\text{3}}} ,{\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}} ,{\text{CI}}^{{\text{ - }}} ,{\text{NH}}_{{\text{3}}} {\left( {{\text{gas}}} \right)},{\text{HNO}}_{{\text{3}}} {\left( {{\text{gas}}} \right)},{\text{NO}}_{2} {\text{and}}{\text{PM}}_{{{\text{10}}}} {\left( {{{\text{PM}}_{{2.5}} } \mathord{\left/ {\vphantom {{{\text{PM}}_{{2.5}} } {{\text{PM}}_{{{\text{10}}}} {\text{ratio}}}}} \right. \kern-\nulldelimiterspace} {{\text{PM}}_{{{\text{10}}}} {\text{ratio}}} = 0.74} \right)}$ covering winter and summer seasons and day and night samplings to capture the diurnal variations. Results showed ${\text{NO}}^{{\text{ - }}}_{{\text{3}}} ,{\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}} ,{\text{NH}}^{{\text{ + }}}_{{\text{4}}} ,{\text{K}}^{ + }$ are found to be significantly high in winter season compared to the summer season. In winter, the molar ratio of ${\text{NH}}^{{\text{ + }}}_{{\text{4}}}$ to ${\text{SO}}^{{{\text{2 - }}}}_{{\text{4}}}$ was found to be greater than 2:1. This higher molar ratio suggests that in addition to (NH₄)₂SO₄, NH₄NO₃ will be formed because of excess quantity of ${\text{NH}}^{{\text{ + }}}_{{\text{4}}}$ present. In summer, the molar ratio was less than 2:1 indicating deficit of ${\text{NH}}^{{\text{ + }}}_{{\text{4}}}$ to produce NH₄NO₃. The nitrogen conversion ratio (NO₂ to NO₃) was found to be nearly 50% in the study area that suggested quick conversion of NO₂ into nitric acid. As an overall conclusion, this study finds that NH₃ plays a vital role in the formation of fine inorganic secondary particles particularly so in winter months and there is a need to identify and assess sources of ammonia emissions in India.

Keywords:	Inorganic secondary particles Ammonia Sulfate Nitrate Water soluble ions India
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