Policies to Address Smog
Such measures such as fuel switching (use of natural gas instead coal), and desulfurization of flue gases of coal-fired power plants have contributed very significantly to reducing sulfur dioxide concentrations to the extent that winter smog episodes have more or less ceased to be a problem in the US and Europe. In some developing countries sulfur dioxide-induced smog is still a problem, e.g. in some cities in Western China like Urumqi. Low-nitrogen oxide-emitting gas and oil burners, car exhaust catalysts, expansion of public rail transport and low-emission application of fertilizer in agriculture have significantly contributed to the abatement of photochemical smog problems—and the frequency of summer smog episodes has gone down in Europe and the US. Strong economic growth in e.g. East Asian countries has induced a large increase in emissions of nitrogen oxides and Volatile Organic Compounds, leading to more air pollution problems due to summer smog.