Toronto area ozone: Long‐term measurements and modeled sources of poor air quality events

Abstract

The University of Toronto Atmospheric Observatory and Environment Canada's Centre for Atmospheric Research Experiments each has over a decade of ground-based Fourier transform infrared (FTIR) spectroscopy measurements in southern Ontario. We present the Toronto area FTIR time series from 2002 to 2013 of two tropospheric trace gases-ozone and carbon monoxide-along with surface in situ measurements taken by government monitoring programs. We interpret their variability with the GEOS-Chem chemical transport model and determine the atmospheric conditions that cause pollution events in the time series. Our analysis includes a regionally tagged O 3 model of the 2004-2007 time period, which quantifies the geographical contributions to Toronto area O 3 . The important emission types for 15 pollution events are then determined with a high-resolution adjoint model. Toronto O 3 , during pollution events, is most sensitive to southern Ontario and U.S. fossil fuel NO x emissions and natural isoprene emissions. The sources of Toronto pollution events are found to be highly variable, and this is demonstrated in four case studies representing local, short-, middle-, and long-range transport scenarios. This suggests that continental-scale emission reductions could improve air quality in the Toronto region. We also find that abnormally high temperatures and high-pressure systems are common to all pollution events studied, suggesting that climate change may impact Toronto O 3 . Finally, we quantitatively compare the sensitivity of the surface and column measurements to anthropogenic NO x emissions and show that they are remarkably similar. This work thus demonstrates the usefulness of FTIR measurements in an urban area to assess air quality.

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