The effect of meteorological and chemical factors on the agreement between observations and predictions of fine aerosol composition in southwestern Ontario during BAQS-Met
Date
2011
Authors
Markovic, M. Z.
Hayden, K. L.
Murphy, J. G.
Makar, P. A.
Ellis, R. A.
Chang, R. Y. -W
Slowik, J. G.
Mihele, C.
Brook, J.
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Abstract
The Border Air Quality and Meteorology Study (BAQS-Met) was an intensive, collaborative
field campaign during the summer of 2007 that investigated the effects of transboundary
pollution, local pollution, and local meteorology on air quality in southwestern
Ontario. This analysis focuses on the measurements of the inorganic constituents of
particulate matter with diameter of less than 1 mu m (PM1), with a specific emphasis on
nitrate. We evaluate the ability of AURAMS, Environment Canada's chemical
transport model, to represent regional air pollution in SW Ontario by comparing modelled
aerosol inorganic chemical composition with measurements from Aerosol Mass Spectrometers
(AMS) onboard the National Research Council (NRC) of Canada Twin Otter aircraft and at a
ground site in Harrow, ON. The agreement between modelled and measured pNO(3)(-) at the
ground site (observed mean (M-obs) = 0.50 mu g m(-3); modelled mean (M-mod) = 0.58 mu g
m(-3); root mean square error (RSME) = 1.27 mu g m(-3)) was better than aloft (M-obs =
0.32 mu g m(-3); M-mod = 0.09 mu g m(-3); RSME = 0.48 mu g m(-3)). Possible reasons for
discrepancies include errors in (i) emission inventories, (ii) atmospheric chemistry,
(iii) predicted meteorological parameters, or (iv) gas/particle thermodynamics in the
model framework. Using the inorganic thermodynamics model, ISORROPIA, in an offline
mode, we find that the assumption of thermodynamic equilibrium is consistent with
observations of gas and particle composition at Harrow. We develop a framework to assess
the sensitivity of PM, nitrate to meteorological and chemical parameters and find that
errors in both the predictions of relative humidity and free ammonia (FA NH3(g) +
pNH(4)(+) - 2 center dot pSO(4)(2-)) are responsible for the poor agreement between
modelled and measured values.
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Citation
Markovic, M. Z., K. L. Hayden, J. G. Murphy, P. A. Makar, et al. 2011. "The effect of meteorological and chemical factors on the agreement between observations
and predictions of fine aerosol composition in southwestern Ontario during BAQS-Met." Atmospheric Chemistry and Physics 11(7): 3195-3210.