The presence of local air pollutants is just one of the ingredients for extreme air pollution episodes; meteorological conditions allowing the accumulation of pollutants are also necessary. Horton et al. (2014) look at how climate change affects the occurrence and persistence of stagnation events using an ensemble of bias-corrected CMIP5 model simulations. They find that by the late 21^st century 55% of the current global population experiences more stagnation events, with up to 40 additional stagnation days per year projected in the majority of the tropics and subtropics. Results here suggest that cuts in local air pollutants such as SO₂ and NO_x, may not improve future air quality as much as expected unless also accompanied by global cuts in carbon emissions.

[For those interested, supplementary details on bias-correction method can be found in: Ashfaq et al. (2010) "Influence of climate model biases and daily-scale temperature and precipitation events on hydrological impacts assessment: A case study of the United States." -- http://onlinelibrary.wiley.com/doi/10.1029/2009JD012965/abstract]