2005–2017 ozone trends and potential benefits of local measures as deduced from air quality measurements in the north of the Barcelona metropolitan area
We analyzed 2005–2017 data sets on ozone (O3)
concentrations in an area (the Vic Plain) frequently affected by the
atmospheric plume northward transport of the Barcelona metropolitan area
(BMA), the atmospheric basin of Spain recording the highest number of
exceedances of the hourly O3 information threshold
(180 µg m−3). We aimed at evaluating the potential benefits
of implementing local-BMA short-term measures to abate emissions of
precursors. To this end, we analyzed in detail spatial and time variations of
concentration of O3 and nitrogen oxides (NO and NO2,
including OMI remote sensing data for the latter). Subsequently, a
sensitivity analysis is done with the air quality (AQ) data to evaluate
potential O3 reductions in the north of the BMA on Sundays compared
with weekdays as a consequence of the reduction in regional emissions of
precursors. The results showed a generalized decreasing trend for regional background
O3 as well as the well-known increase in urban O3 and higher
urban NO decreasing slopes compared with those of NO2. The most
intensive O3 episodes in the Vic Plain are caused by (i) a relatively
high regional background O3 (due to a mix of continental,
hemispheric–tropospheric and stratospheric contributions); by (ii) intensive
surface fumigation from mid-troposphere high O3 upper layers arising
from the concatenation of the vertical recirculation of air masses; but also
by (iii) an important O3 contribution from the northward
transport/channeling of the pollution plume from the BMA. The high relevance
of the local-daily O3 contribution during the most intense pollution
episodes is clearly supported by the O3 (surface concentration) and
NO2 (OMI data) data analysis. A maximum decrease potential (by applying short-term measures to abate
emissions of O3 precursors) of 49 µg O3 m−3
(32 %) of the average diurnal concentrations was determined. Structurally
implemented measures, instead of episodically, could result in important
additional O3 decreases because not only the local O3 coming
from the BMA plume would be reduced, but also the recirculated O3 and
thus the intensity of O3 fumigation in the plain. Therefore, it is
highly probable that both structural and episodic measures to abate
NOx and volatile organic compound (VOC) emissions in the BMA
would result in evident reductions of O3 in the Vic Plain.
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