2005–2017 ozone trends and potential benefits of local measures as deduced from air quality measurements in the north of the Barcelona metropolitan area

Abstract

Abstract. 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.

Increase in secondary organic aerosol in an urban environment

“…S17 points out that O 3 is more reactive in period B, as the area of the difference between PR concentrations and those in the regional background site MSY (Montseny Natural Park, 720 m a.s.l., 40 km north-northeast of Barcelona and 25 km from the Mediterranean coast) is higher during period B. This corresponds to the previously reported observation that O 3 diel concentrations are flatter in MSY because mountain sites are less affected by NO titration, leading to high daily O 3 average concentrations (Massagué et al, 2019). Therefore, the higher the difference is between MSY and PR, the more O 3 has been reacting at PR.…”

Lessons from the COVID-19 air pollution decrease in Spain: Now what?

“…Our O 3 decrease/increase stimates are subject to higher uncertainty than those of other pollutants due to the photochemical dependence of O 3 , the specific meteorological scenarios favoring O 3 episodes in the Mediterranean ( Millán et al, 1997 , Millán et al, 2002 ; Gangoiti et al, 2001 ; Millán, 2014 ; Querol et al, 2017 , Querol et al, 2018 ; Massagué et al, 2019 , among others), and the marked inter-annual variability. However, the results suggest a generalized decrease in 8hDMA O 3 , which was more pronounced in E Spain.…”

Rethinking the role of transport and photochemistry in regional ozone pollution: Insights from ozone mass and concentration budgets

“…More specially, through the vertical exchange in the morning, O3 in the residual layer and/or free atmosphere is entrained into the ABL, leading to the rapid increase of O3 concentration after sunrise (Kaser et al, 2017;Hu et al, 2018;Zhao et al, 2019). Transported O3 may be derived from local sources, or transported from other regions, continents and even stratosphere under the combined effect of meso-, synoptic-, large-and global-scale atmospheric movements (Massagué et al, 2019). In addition, O3 precursors may also be transported into the region and involved in O3 production.…”