Determination of tropospheric vertical columns of NO2 and aerosol optical properties in a rural setting using MAX-DOAS 1Centre for Atmospheric Chemistry, York University, Toronto, ON, Canada
13 Dec 2011
2Satellite Group, Max Planck Institute for Chemistry, Mainz, Germany
3Air Quality Research Division, Environment Canada, Toronto, ON, Canada
4Ontario Ministry of the Environment, Toronto, ON, Canada
5School of Energy and Environment, City U, Hong Kong, China
*now at: Department of Chemistry, University of Toronto, Toronto, ON, Canada
Received: 15 Mar 2011 – Published in Atmos. Chem. Phys. Discuss.: 27 Apr 2011Abstract. Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS)
measurements were performed in a rural location of southwestern Ontario
during the Border Air Quality and Meteorology Study. Slant column densities
(SCDs) of NO2 and O4 were determined using the standard DOAS technique.
Using a radiative transfer model and the O4 SCDs, aerosol optical depths
were determined for clear sky conditions and compared to OMI, MODIS, AERONET,
and local PM2.5 measurements. This aerosol information was input to a
radiative transfer model to calculate NO2 air mass factors, which were fit
to the measured NO2 SCDs to determine tropospheric vertical column
densities (VCDs) of NO2. The method of determining NO2 VCDs in
this way was validated for the first time by comparison to composite VCDs
derived from aircraft and ground-based measurements of NO2. The new
VCDs were compared to VCDs of NO2 determined via retrievals from the
satellite instruments SCIAMACHY and OMI, for overlapping time periods. The
satellite-derived VCDs were higher, with a mean bias of
+0.5–0.9×1015 molec cm−2. This last finding is
different from previous studies whereby MAX-DOAS geometric VCDs were higher
than satellite determinations, albeit for urban areas with higher VCDs. An
effective boundary layer height, BLHeff, is defined as the ratio of
the tropospheric VCD and the ground level concentration of NO2. Variations
of BLHeff can be linked to time of day, source region, stability of
the atmosphere, and the presence or absence of elevated NOx sources.
In particular, a case study is shown where a high VCD and BLHeff
were observed when an elevated industrial plume of NOx and SO2
was fumigated to the surface as a lake breeze impacted the measurement site.
High BLHeff values (~1.9 km) were observed during a regional
smog event when high winds from the SW and high convection promoted mixing
throughout the boundary layer. During this event, the regional line flux of
NO2 through the region was estimated to be greater than 112 kg
NO2 km−1 h−1.
Revised: 25 Nov 2011 – Accepted: 01 Dec 2011 – Published: 13 Dec 2011
Citation: Halla, J. D., Wagner, T., Beirle, S., Brook, J. R., Hayden, K. L., O'Brien, J. M., Ng, A., Majonis, D., Wenig, M. O., and McLaren, R.: Determination of tropospheric vertical columns of NO2 and aerosol optical properties in a rural setting using MAX-DOAS, Atmos. Chem. Phys., 11, 12475-12498, doi:10.5194/acp-11-12475-2011, 2011.