Role of atmospheric ammonia in particulate matter formation in Houston during summertime

摘要

Simultaneous high-time-resolution measurements of atmospheric NH_3, HNO_3, soluble gas-phase chloride, and aerosol species were made in Houston, TX, from August 5, 2010 to August 9, 2010. Gaseous NH_3 was measured using a 10.4-μm external cavity quantum cascade laser-based sensor employing conventional photo-acoustic spectroscopy, while gaseous HNO_3 and HC1 were sampled using a mist chamber-ion chromatograph (IC) system. Particle chemical composition was determined using a particle-into-liquid-sampler-IC system. There was a large amount of variability in the gas phase mixing ratios of NH_3 (3.0 ± 2.5 ppb), HNO_3 (287.4 ± 291.6 ppt), and HCl (221.3 ± 260.7 ppt). Elevated NH_3 levels occurred around mid-day when NH_4~+ (0.5± 1.0 μg m~(-3)) and SO_4~(2-)(4.5 ± 4.3 μg m~(-3)) also increased considerably, indicating that NH_3 likely influenced aerosol particle mass. By contrast, the formation of NH_4NO_3 and NH_4Cl was not observed during the measurements. Point sources (e.g., power plant and chemical plant) might be potential contributors to the enhancements in NH_3 at the measurement site under favorable meteorological conditions. Increased particle number concentrations were predicted by the SAM-TOMAS model downwind of a large coal-fired power plant when NH_3 emissions (based on these measurements) were included, highlighting the potential importance of NH_3 with respect to particle number concentration. Separate measurements also indicate the role of NH_3 in new particle formation in Houston under low-sulfur conditions.