Mobile sources of emissions

While the traditional image of air pollution is still associated with a large industrial stack belching black smoke, the majority of urban air pollution comes from:   transport, that is mobile emission sources. Cars and their internal combustion engines, but also trains, ships and aircraft all burn considerable amounts of fuel and do contribute significantly to air pollution both locally but also on a global scale.   Some of the complexities of addressing the transportation system include:

• Highly dynamic nature of these emissions: the sources move, even though along well defined paths;
• The transient nature: these movements usually exhibit well defined patterns in time (the urban rush hour being an obvious example) with the resulting short-term maxima, usually underestimated with any long-term average representation;
• A strong psychological element attached to individual freedom of movement (and private cars) that makes any limitations for individual passenger cars usually rather controversial.

Road traffic:   is usually the major contributor to urban air pollution with anything from 50 to 80% of total emissions. In addition, emisison from traffic are near ground level, and this will create much higher values of local ambient ground level pollution people are exposed to as compared to elevated industrial stacks.
European (EMEP) emission factor (2009): depending on engine size, speed but also driving style, emissions (in g/km) may range from as low as 0.01 g/km for a EURO_4 hybrid gasoline vehicle up to 12.8 g/km or, at average speed, 0.05 g/s for NOx for older, pre-ECE HDV. The most common compact passenger car (EURO-4) would contribute between 0.09 and 0.02 g/km, depending on speed.

Railways:   Diesel engines are the predominant form of power unit within the railways industry, in particular for the long haul, over large distances where electrification would be costly. With engine power up to 4,000 KW, typical fuel consumption for line haul locomotives would be in the order of hundred to 250 kilo of fuel oil per hour, translating into emission values of 1-4 g NOx/s.

Shipping:   Marine diesel engines are the predominant form of power unit within the marine industry for both propulsion and auxiliary power generation. In 2010 an analysis of about 100 000 vessels indicated marine diesels powered around 99 % of the world<92>s fleet, with steam turbines powering less than 1 %. The only other type of engine highlighted was gas turbines, used virtually only on passenger vessels, and only used in around 0.1 % of vessels (Trozzi, 2010). Diesel engines can be categorized into slow (around 18% of engines), medium (around 55%), or fast (around 27%), depending on their rated speed.

Air transport:   Aviaton activities can be grouped into:

• Category 1 - Civil instrument flight rule (IFR) flights; this includes the majority of commercial air transport;
• Category 2 - Civil visual flight rule (VFR) flights, or general aviation; contains small aircraft used for leisure, agriculture, taxi flights, etc.
• Category 3 - Civil helicopters;
• Category 4 - Operational military flights.

Relevant EC Directives include:

• EC Directive 98/70/EC (on the quality of diesel fuels)
• EC Directive 1999/32/EC (reduction of sulphur content in liquid fuels)
• EC Directive 2003/44/EC (diesel, 2-stroke gasoline and 4-stroke gasoline engines)
• EC Directive 2005/33/EC (amending 1999/32/EC)
• http://ec.europa.eu/clima/documentation/transport/aviation/index_en.htm)
• EC Directive 2008/101/EC amending Directive 2003/87/EC incluingd aviation in the scheme for greenhouse gas emission allowance trading
• COMMISSION REGULATION (EU) No 82/2010 on the list of aircraft operators
• Commission Decision 2009/450/EC on aviation activities listed in the Annex I to Directive 2003/87/EC
• Commission Decision 2009/339/EC on monitoring and reporting guidelines for emissions

PUFF: sensitivity analysis