Abstract
Abstract. In order to improve the current understanding of the dynamics of ammonia (NH3) in a major industrial and urban area, intensive measurements of atmospheric NH3 were conducted in Houston during two sampling periods (12 February 2010–1 March 2010 and 5 August 2010–25 September 2010). The measurements were performed with a 10.4-μm external cavity quantum cascade laser (EC-QCL)-based sensor employing conventional photo-acoustic spectroscopy. The mixing ratio of NH3 ranged from 0.1 to 8.7 ppb with a mean of 2.4 ± 1.2 ppb in winter and ranged from 0.2 to 27.1 ppb with a mean of 3.1 ± 2.9 ppb in summer. The larger levels in summer probably are due to higher ambient temperature. A notable morning increase and a mid-day decrease were observed in the diurnal profile of NH3 mixing ratios. Motor vehicles were found to be major contributors to the elevated levels during morning rush hours in winter. However, changes in vehicular catalytic converter performance and other local or regional emission sources from different wind directions governed the behavior of NH3 during morning rush hours in summer. There was a large amount of variability, particularly in summer, with several episodes of elevated NH3 mixing ratios that could be linked to industrial facilities. A considerable discrepancy in NH3 mixing ratios existed between weekdays and weekends. This study suggests that NH3 mixing ratios in Houston occasionally exceeded previous modeling predictions when sporadic and substantial enhancements occurred, potentially causing profound effects on particulate matter formation and local air quality.
Highlights
As the third most abundant nitrogen-containing compound and predominant gaseous base in the atmosphere, ammonia (NH3) plays an important role in atmospheric chemistry
From a perspective of environmental concern, NH3 is a precursor of particulate matter (PM) because it can lead to the production of ammonium salts (e.g. (NH4)2SO4, NH4HSO4, and NH4NO3) through chemical reactions with sulfuric and nitric acid formed by oxidation of sulfur dioxide and nitrogen oxides, respectively (Sutton et al, 2008)
In this work we demonstrated atmospheric NH3 measurement results using a 10.4-μm external cavity quantum cascade laser (EC-QCL)-based sensor employing conventional photo-acoustic spectroscopy with a minimum detection limit below 1 ppb
Summary
As the third most abundant nitrogen-containing compound and predominant gaseous base in the atmosphere, ammonia (NH3) plays an important role in atmospheric chemistry. It has many anthropogenic (e.g. agricultural crops, mineral fertilizers, and biomass burning) and natural (e.g. animals, oceans, and vegetation) sources in the environment. (NH4)2SO4, NH4HSO4, and NH4NO3) through chemical reactions with sulfuric and nitric acid formed by oxidation of sulfur dioxide and nitrogen oxides, respectively (Sutton et al, 2008). Formation of these salts may lead to homogeneous aerosol nucleation (McMurry et al, 2005).
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