Publication Date:
2013-07-25
Description:
[1] During the Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) campaign at the National Oceanic and Atmospheric Administration Boulder Atmospheric Observatory tower, Erie, CO, USA in winter 2011, soluble trace gases, the ionic composition of size-resolved aerosols, and the associated meteorological conditions were measured. Median gas-phase mixing ratios of HCl, HNO 3 and NH 3 measured via tandem mist chambers were 0.072, 0.202, and 5.79 respectively. Most Cl - was associated with super- μ m size fractions whereas NO 3 - and NH 4 + were associated primarily with sub- μ m size fractions. Aerosol pHs inferred from the measured phase partitioning and thermodynamic properties of HNO 3 and NH 3 were similar both in terms of absolute values and variability as a function of size. Aerosols were acidic across all size fractions and throughout the duration of the campaign (mostly in the pH range of 2 to 3). pHs inferred from the HCl/Cl - couple were consistently higher by about 1 to 2 pH units suggesting possible bias in the associated thermodynamic evaluation of HCl. Specifically, relative to those for HNO 3 and NH 3 , the Henry's Law constant for HCl is associated with much greater uncertainty. Condensation of HCl replaced Cl - consumed in the ClNO 2 production. Additionally, total Cl (HCl + Cl - ) was greater than ClNO 2 in sampled air parcels suggesting that Cl availability was not the limiting factor in ClNO 2 production. Median ClNO 2 yields from N 2 O 5 reaction with particulate Cl- associated with all size fractions were greater than 0.9.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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