1 research outputs found
The changing oxidizing environment in London – trends in ozone precursors and their contribution to ozone production
Ground-level ozone is recognized to be a threat to human health (WHO, 2003), have
a deleterious impact on vegetation (Fowler et al., 2009), is also an important greenhouse
gas (IPCC, 2007) and key to the oxidative ability of the atmosphere (Monks et al.,
5 2009). Owing to its harmful effect on health, much policy and mitigation effort has been
put into reducing its precursors – the nitrogen oxides (NOx
) and non-methane volatile
organic compounds (NMVOCs). The non-linear chemistry of tropospheric ozone formation,
dependent mainly on NOx and NMVOC concentrations in the atmosphere, makes
controlling tropospheric ozone complex. Furthermore, the concentration of ozone at
10 any given point is a complex superimposition of in-situ produced or destroyed ozone
and transported ozone on the regional and hemispheric-scale. In order to effectively address
ozone, a more detailed understanding of its origins is needed. Here we show that
roughly half (5 µgm−3
) of the observed increase in urban (London) ozone (10 µgm−3
)
in the UK from 1998 to 2008 is owing to factors of local origin, in particular, the change
in NO : NO2
15 ratio, NMVOC : NOx balance, NMVOC speciation, and emission reductions
(including NOx
titration). In areas with previously higher large concentrations of nitrogen
oxides, ozone that was previously suppressed by high concentrations of NO has
now been “unmasked”, as in London and other urban areas of the UK. The remaining
half (approximately 5 µgm−3
) of the observed ozone increase is attributed to non-local
20 factors such as long-term transport of ozone, changes in background ozone, and meteorological
variability. These results show that a two-pronged approach, local action
and regional-to-hemispheric cooperation, is needed to reduce ozone and thereby population
exposure, which is especially important for urban ozone