AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Gas-Particle Partitioning of Ammonia in the Fort Worth, TX Area
LONGWEN GONG, Rafal Lewichi, Robert Griffin, Andrew Rutter, Frank Tittel, Barry Lefer, James Flynn, Jack Dibb, Eric Scheuer, Rice University
Abstract Number: 127 Working Group: Aerosol Chemistry
Abstract In order to investigate the dynamics of ammonia in a suburban area expected by urban, industrial, and biogenic sources, intensive measurements of atmospheric ammonia were made northwest of Fort Worth, TX. The mixing ratio of ammonia ranged from 0.1 to 10.1 ppb with a mean of 2.7+/-1.7 ppb. A daytime increase was found, likely due to increasing ambient temperatures affecting temperature-dependent sources such as volatilization of animal waste and vegetation. Ammonia mixing ratios reached maximum values in the early afternoon, after which they decreased and remained relatively low during nighttime. Simultaneous measurements of aerosol and other gaseous species also were conducted. Particulate ammonium concentrations varied from 0.1 to 2.5 microgram/m$^3 with a mean of 0.5+/-0.2 microgram/m$^3, nitrate concentrations varied from 0.1 to 1.1 microgram/m$^3 with a mean of 0.2+/-0.1 microgram/m$^3, and sulfate concentrations varied from 0.2 to 6.0 microgram/m$^3 with a mean of 1.2+/-0.6 microgram/m$^3, respectively. Gaseous nitric acid levels ranged from 0.05 to 5.0 ppb with an average of 0.5+/-0.5 ppb and hydrochloric acid levels ranged from 0.03 to 2.0 ppb with an average of 0.4+/-0.3 ppb. The diurnal profile of the ratio of ammonia to total ammonia (=ammonia+ammonium) exhibited a similar trend to gaseous ammonia, and was anti-correlated with sulfate. Ammonia was present predominantly in the gas phase. The formation of ammonium nitrate and ammonium chloride was not observed; ammonium mainly existed in the form of ammonium sulfate. In addition, ambient aerosols were nearly neutral, indicating that sufficient ammonia was available to neutralize sulfuric acid in the atmosphere.