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Associated topic: acidification, eutrophication, photochemical pollution, greenhouse effet

Emissions monitoring period: since 1960

Data source: CITEPA / SECTEN format - April 2017


Sources of the pollutant

Nitrogen oxides (generally defined as NOx = NO + NO2) are mainly released, like SO2, by fossil fuel combustion and by some industrial processes (production of nitric acid, fertiliser manufacture, surface treatments, etc.). Their formation, mainly in combustion chambers, is the result of three different mechanisms that produce:

    • Thermal NOx

N2 (air) + O2 → 2 NO when the temperature rises above 1400°C

    • Fuel NOx

R-NH2 (combined nitrogen in fuel) + O2 → NO + ... if N combined in the fuel

    • Prompt NOx

N2 + CH → HCN + N then NO in different stages, even at lower temperatures

When oxygen is present in the combustion chamber, 0.5 to 10% of NO is transformed into NO2. This reaction proceeds slowly in the atmosphere and, in cities with heavy traffic, in combination with dust, it is responsible, for the brownish colour of polluted air layers a few hundred metres above the ground. NOx are also involved in the formation of photochemical oxidants (tropospheric ozone) and indirectly accentuate the greenhouse effect.

The sectors emitting the most NOx are road transport (hence the policy for reducing emissions by means of catalytic converters, for example) and large combustion plants (LCP). Volcanoes, thunderstorms and forest fires also contribute to NOx emissions.


Effect of the pollutant

NO2 is toxic (40 times more than CO, 4 times more than NO), and penetrates deep into the lungs. Peak concentrations are more harmful than exposure to the same dose over a long period of time. NO is a gas that irritates the bronchial passages and reduces oxygen uptake from blood.


Classification of the sub-sectors with the highest emission levels* in 2015

Classification Sub-sectors Share of the sub-sector in total national emissions in mainland France
1 Diesel-fuelled passenger cars 24%
2 Diesel-fuelled heavy-duty vehicles (including buses and coaches) 18%
3 Diesel-fuelled light-duty vehicles 12%
4 Other agricultural sources (combustion plants and off-road mobile machinery) 7.9%
5 Residential sector 7.0%

*: one sector (out of six: energy transformation, manufacturing industry, residential/tertiary, agriculture/forestry, road and other transport) is broken down into sub-sectors.


Emissions and trends

Minimum observed: 835 kt in 2015
Maximum observed: 2 045 kt in 1979
Emissions in 2015: 835 kt
Trends 2015/1980: -58.8%
Trends 2015/1990: -57.1%
Trends 2015/maximum: -59.1%
Trends 2015/minimum: 0%

Measurement unit: kt (kilotonne)
N.B. : emissions include those from combustion and from processes.
Source CITEPA / SECTEN format – April 2017


Graph NOx 17

Graph Legende sans UTCFv2

Source CITEPA / SECTEN format – April 2017

Tab NOx 17

(*) Following UNECE/NEC definitions : emissions classified "except total" are not included, i.e. emissions from international maritime, emissions from domestic and international air transport cruise (≥ 1000 m), emissions from agriculture and forestry biogenic sources and emissions from non-anthropogenic sources.
(e) preliminary estimate 



Since 1966, road transport has been the main contributing sector to NOx emissions. The associated emissions were... (to read more, consult the SECTEN report online via your login and password)


Data source: CITEPA / SECTEN format - April 2017