Measurements of HONO during BAQS-Met 1Department of Chemistry, York University, Toronto, Ontario, Canada
2Centre for Atmospheric Chemistry, York University, Toronto, Ontario, Canada
*now at: Environment Canada, Science and Technology Branch, Toronto, ON, Canada
**now at: Environment Canada, Science and Technology Branch, Vancouver, BC, Canada
Received: 30 April 2010 – Published in Atmos. Chem. Phys. Discuss.: 21 June 2010 Abstract. Measurements of nitrous acid (HONO) were performed as part of the 2007
Border Air Quality and Meteorology Study (BAQS-Met) at the Harrow, Ontario,
Canada supersite between 20 June and 10 July 2007. Nitrous acid is an
important precursor of the hydroxyl radical and understanding its chemistry
is important to understanding daytime oxidation chemistry. The HONO
measurements were made using a custom built Long Path Absorption Photometer
(LOPAP). The goal of this work was to shed light on sources of daytime HONO
in the border region. During the course of the campaign HONO mixing ratios
consistently exceeded expected daytime values by more than a factor of 6.
Mean daytime mixing ratios of 61 pptv were observed. While HONO decay began
at sunrise, minimum HONO values were measured during the late afternoon.
There was little difference between the daytime (mean = 1.5%) and
night-time (mean = 1.7%) ratios of HONO/NO2, thus there was a very
strong daytime source of HONO which is consistent with other recent studies.
Correlations of daytime HONO production with a variety of chemical and
meteorological parameters indicate that production is dependent on UV
radiation, NO2 and water vapour but is not consistent with a simple gas
phase process. Apparent rate constants for the production of HONO from
photolyticaly excited NO2 and water vapour vary from
2.8–7.8×10−13 cm3 molec−1 s−1,
during the campaign. These results appear to be consistent with
the heterogeneous conversion of NO2 enhanced by photo-excitation.
Revised: 29 November 2010 – Accepted: 03 December 2010 – Published: 23 December 2010
Citation: Wentzell, J. J. B., Schiller, C. L., and Harris, G. W.: Measurements of HONO during BAQS-Met, Atmos. Chem. Phys., 10, 12285-12293, doi:10.5194/acp-10-12285-2010, 2010.