资源环境科技发展态势分析平台

Various studies have reported that the photochemical nucleation of new ultrafine particles (UFPs) in urban environments within high insolation regions occurs simultaneously with high ground ozone (O-3) levels. In this work, we evaluate the atmospheric dynamics leading to summer O3 episodes in the Madrid air basin (central Iberia) by means of measuring a 3-D distribution of concentrations for both pollutants. To this end, we obtained vertical profiles (up to 1200m above ground level) using tethered balloons and miniaturised instrumentation at a suburban site located to the SW of the Madrid Metropolitan Area (MMA), the Majada-honda site (MJDH), in July 2016. Simultaneously, measurements of an extensive number of air quality and meteorological parameters were carried out at three supersites across the MMA. Furthermore, data from O-3 soundings and daily radio soundings were also used to interpret atmospheric dynamics.

The results demonstrate the concatenation of venting and accumulation episodes, with relative lows (venting) and peaks (accumulation) in O-3 surface levels. Regardless of the episode type, the fumigation of high-altitude O-3 (arising from a variety of origins) contributes the major proportion of surface O-3 concentrations. Accumulation episodes are characterised by a relatively thinner planetary boundary layer (<1500m at midday, lower in altitude than the orographic features), light synoptic winds, and the development of mountain breezes along the slopes of the Guadarrama Mountain Range (located W and NW of the MMA, with a maximum elevation of >2400ma.s.l.). This orographic-meteorological setting causes the vertical recirculation of air masses and enrichment of O-3 in the lower tropospheric layers. When the highly polluted urban plume from Madrid is affected by these dynamics, the highest Ox (O-3 + NO2) concentrations are recorded in the MMA.

Vertical O-3 profiles during venting episodes, with strong synoptic winds and a deepening of the planetary boundary layer reaching > 2000ma.s.l., were characterised by an upward gradient in O-3 levels, whereas a reverse situation with O-3 concentration maxima at lower levels was found during the accumulation episodes due to local and/or regional production. The two contributions to O-3 surface levels (fumigation from high-altitude strata, a high O-3 background, and/or regional production) require very different approaches for policy actions. In contrast to O-3 vertical top-down transfer, UFPs are formed in the planetary boundary layer (PBL) and are transferred upwards progressively with the increase in PBL growth.