A Sea Level Stratospheric Ozone Intrusion Event Induced within a Thunderstorm Gust Front

Abstract

Ozone from a stratospheric intrusion (SI) reached sea level in association with a thunderstorm gust front during the predawn hours of 16 April 2018. The event caused surface ozone concentration increases of 30 to more than 50 ppbv in a matter of minutes in a band from approximately Richmond, Virginia, to Philadelphia, Pennsylvania. Peak hourly ozone concentrations reached 74 ppbv in northeastern Maryland despite absent photochemistry and ongoing convective activity. An intense jet stream with velocities >80 kt (41 m s−1) less than 1 km above ground level was observed associated with a deepening cyclone. Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), showed a filament of ozone with concentrations greater than 90 ppbv extending downward from the stratosphere to the lower troposphere. This SI filament became collocated with an ongoing severe squall line, and stratospheric ozone was transported directly to sea level when entrained into the squall-line gust front. Weather radar and in situ observations confirmed surface ozone increased with the thunderstorm gust front, while a concurrent reduction in carbon monoxide confirmed air within the gust front had stratospheric origins. While rare, such coupling events are important to troposphere–stratosphere exchanges and in overall atmospheric chemistry and climate. This may be the first event of its type and magnitude documented.

Stratospheric influence on surface ozone pollution in China

“…Stratospheric air is characterized by high O 3 , low carbon monoxide (CO), and low relative humidity (RH) 3,4,24 . Intrusions of stratospheric air downward to the surface level produce sharp upward (downward) spikes in the surface-measured O 3 (CO), as documented in many case studies [6][7][8][9] . Such stratospheric signals can provide a clear indication of SI that have reached the surface level with the aid of dense surface observations.…”

“…Low RH may also appear when air parcels descend from higher altitudes to the lower troposphere experiencing adiabatic warming. The air parcels can also experience various atmospheric moisture conditions on their way to the surface, so RH of the air parcels is less conservative than O 3 and CO 3 , 8 . In addition, concurrent RH measurements are usually unavailable in air quality monitoring stations in China.…”

“…The instantaneous and local nature of SITS events 3 requires comprehensive observations with a high spatial and temporal resolution in order to assess their impacts on surface O 3 . The routine weekly ozonesonde observations can directly monitor vertical O 3 variation, they are not able to capture SITS events that persist only for several hours 4 , 8 , 9 . Running multi-instrumental campaigns with targeted stratospheric tracers, such as O 3 and cosmogenic radionuclide, can provide reliable indicators of SITS 5 , 22 , 23 .…”

“…Though the injected stratospheric O 3 is estimated to account for only 5-10% of the tropospheric O 3 sources 2 , case studies of stratospheric intrusions (SI) to the troposphere have documented how SI occurred and impacted tropospheric and even surface O 3 [3][4][5] . Events of deep and fast stratospheric intrusions to the surface (SITS) can lead to high-O 3 episodes, inducing severe O 3 pollution [6][7][8][9] . In the recent decade, China has confronted a severe O 3 pollution problem, even after the implementation of strict policies on emission reductions of O 3 precursors.…”

Augmenting the Standard Operating Procedures of Health and Air Quality Stakeholders With NASA Resources

“…While the weather systems that lead to these “stratospheric intrusions” occur year‐round, there is a build‐up of O 3 in the lower stratosphere during late winter and early spring, which increases O 3 concentrations within intrusions. These events are most likely to directly influence communities at high elevations, as there is less distance between ground‐level and the stratosphere, but the stratospheric air can reach sea‐level when associated with convective systems (Dreessen, 2019 ) or if the filament remains intact and descends to the surface in a subsequent weather system (Knowland, Doherty, et al., 2017 ). Because these events are associated with distinct weather phenomena, AQ managers use weather forecasts to identify regions where a stratospheric intrusion is likely to happen.…”