Air quality and climate in North America: current and 2050

Two numerical models, the Canadian Regional Climate Model (CRCM, v4.2.3), and A Unified Regional Air-quality Modelling System (AURAMS, v1.3.2, beta rev 463), have been linked to study the effects of climate change on air pollution over a North American Domain at 45km resolution. The CRCM, a limited-area model driven at the boundaries by fields from the Canadian Coupled General Circulation Model (CGCM v3.1), provided the driving meteorology on fifteen minute time steps for the off-line AURAMS model. AURAMS is a comprehensive air pollution chemical transport model, including size- and species-resolved particulate matter (12 sections, 9 chemical species), gas-phase chemistry, inorganic and organic heterogeneous chemistry, aqueous chemistry, and the emissions, transport and removal of both gases and particles.

Two periods were chosen for simulations, ten “current climate” summers (June-July-August) from 1997 to 2006, and ten “future climate” summers, from 2041 to 2050. These were matched with current emissions (2002 Canadian and USA, 1999 Mexican inventories), and future emissions (2020 current legislation projections, further projected to 2050 based on RCP 6 scenarios). Three sets of simulations were constructed: “Current climate, current emissions”, “future climate, future emissions”, and “future climate, future emissions”.

The current climate, current emissions scenarios were evaluated against observational data from North American monitoring networks for ozone and PM2.5 (1023 ozone stations, 278 PM2.5 stations). Standard statistical measures of model performance were used to describe the coupled modelling system's performance for these pollutants. The climate model is free-running (unlike a data assimilation/weather forecast system), hence comparisons were made on the basis of climatological averages. A summary of the CRCM's ability to reproduce the current North American climate will also be presented.

Comparisons between the (current climate, current emissions) scenario and the remaining two scenarios were used to estimate the impact of climate change alone, and of the combination of climate change and emissions projections, on air-quality. These results were compared to other projections found in the literature.