Measurement and Analysis of the Relationship between Ammonia,Acid Gases,and Fine Particles in Eastern North Carolina

Abstract

An annular denuder system, which consisted of a cyclone separator; two diffusion denuders coated with sodium carbonate and citric acid, respectively; and a filter pack consisting of Teflon and nylon filters in series, was used to measure acid gases, ammonia (NH₃), and fine particles in the atmosphere from April 1998 to March 1999 in eastern North Carolina (i.e., an NH₃?rich environment). The sodium carbonate denuders yielded average acid gas concentrations of 0.23 μg/m³ hydrochloric acid (standard deviation SD] ± 0.2 μg/m³); 1.14 μg/m³ nitric acid (SD ± 0.81 μg/m³), and 1.61 μg/m³ sulfuric acid (SD ± 1.58 μg/m³). The citric acid denuders yielded an average concentration of 17.89 μg/m³ NH₃ (SD ± 15.03 μg/m³). The filters yielded average fine aerosol concentrations of 1.64 μg/m³ ammonium (NH₄ ⁺;SD ± 1.26 μg/m³); 0.26 μg/m³ chloride (SD ± 0.69 μg/m³), 1.92 μg/m³ nitrate (SD ± 1.09 μg/m³), and 3.18 μg/m³ sulfate (SO₄ ^2?; SD ± 3.12 μg/m³). From seasonal variation, the measured particulates (NH₄ ⁺,SO₄ ^2?, and nitrate) showed larger peak concentrations during summer, suggesting that the gas-to-particle conversion was efficient during summer. The aerosol fraction in this study area indicated the domination of ammonium sulfate particles because of the local abundance of NH₃, and the long-range transport of SO₄ ^2? based on back trajectory analysis. Relative humidity effects on gas-to-particle conversion processes were analyzed by particulate NH₄ ⁺ concentration originally formed from the neutralization processes with the secondary pollutants in the atmosphere.