Legal Air Quality Roadside Standards Ignored

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Many European countries do not meet legal air quality standards for ambient nitrogen dioxide (NO₂) near roads; a problem that has been forecasted to persist to 2030

Although European air quality standards regulate NO₂ concentrations, emissions standards for new vehicles instead set limits for NO x - the combination of nitric oxide (NO) and NO₂. From around 1990 onwards, the total emissions of NO x declined significantly in Europe but roadside concentrations of NO₂ declined much less than expected.

This discrepancy has been attributed largely to the increasing usage of diesel vehicles in Europe and more directly emitted tailpipe NO₂. A survey applied a data-filtering technique to 130 million hourly measurements of NO x, NO₂ and ozone (O₃) from roadside monitoring stations across 61 urban areas in Europe over the period 1990–2015 to estimate the continent-wide trends of directly emitted NO₂. It was found that the ratio of NO₂ to NO x emissions increased from 1995 to around 2010 but has since stabilised at a level that is substantially lower than is assumed in some key emissions inventories.

The proportion of NO x now being emitted directly from road transport as NO₂ is up than the estimates used in policy projections.

Picture: Air quality standards across Europe is, if not going backward, certainly not progressing in line with targets

Article written by Stuart K. Grange, Alastair C. Lewis, Sarah J. Moller & David C. Carslaw

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