In Europe, air pollution is primarily a result of the combustion of hydrocarbons in road transport and heating. In urban areas, emission of NOx, and NO2 in particular are primarily the result of road transport. Secondly, emissions from household and commercial heating are known as “low-stack emissions” (when the point of origin is below 40m), and are caused largely by the use of low quality heating fuels, and old furnaces. Furthermore, low stack emissions are the primary contributor to the creation of excessive amounts of PM2.5, PM10 and benzo(a)pyrene. Although transport and heating represent a large potential for improvement in air quality, actual progress is limited by 4 major group of factors: technology, market incentives, public policies and awareness. The main source of smog also differs by region. In Western Europe, for example, it originates primarily from transportation. By contrast, in Eastern Europe, the main source of smog is heating (and to a lesser extent, transportation). As a result, the smog problem in Europe may also be considered to be further complicated by regionalization.