Abstract
Much progress has been made in creating satellite products for tracking the pollutants ozone and NO2 in the troposphere. Yet, in mid-latitude regions where meteorological interactions with pollutants are complex, accuracy can be difficult to achieve, largely due to persistent layering of some constituents. We characterize the layering of ozone soundings and related species measured from aircraft over two ground sites in suburban Washington, DC (Beltsville, MD, 39.05 N; 76.9 W) and Baltimore (Edgewood, MD, 39.4 N; 76.3 W) during the July 2011 DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) experiment. First, we compare column-ozone amounts from the Beltsville and Edgewood sondes with data from overpassing satellites. Second, processes influencing ozone profile structure are analyzed using Laminar Identification and tracers: sonde water vapor, aircraft CO and NOy. Third, Beltsville ozone profiles and meteorological influences in July 2011 are compared to those from the summers of 2006–2010. Sonde-satellite offsets in total ozone during July 2011 at Edgewood and Beltsville, compared to the Ozone Monitoring Instrument (OMI), were 3 % mean absolute error, not statistically significant. The disagreement between an OMI/Microwave Limb Sounder-based tropospheric ozone column and the sonde averaged 10 % at both sites, with the sonde usually greater than the satellite. Laminar Identification (LID), that distinguishes ozone segments influenced by convective and advective transport, reveals that on days when both stations launched ozonesondes, vertical mixing was stronger at Edgewood. Approximately half the lower free troposphere sonde profiles have very dry laminae, with coincident aircraft spirals displaying low CO (80–110 ppbv), suggesting stratospheric influence. Ozone budgets at Beltsville in July 2011, determined with LID, as well as standard meteorological indicators, resemble those of 4 of the previous 5 summers. The penetration of stratospheric air throughout the troposphere appears to be typical for summer conditions in the Baltimore-Washington region.
Highlights
Ground-level ozone is a routinely monitored pollutant in the US, important information about regional and intra- and inter-regional transport comes from measurements of ozone profiles because they encompass the levels in the middle and lower troposphere at which transport occurs
This study addresses the following questions: 1. How do satellite-derived ozone column estimates compare to the Beltsville and Edgewood soundings? Ozone Monitoring Instrument (OMI) total ozone and the OMI/MLS trajectory-enhanced tropospheric ozone residual (TTOR) products are evaluated
The Beltsville soundings were made with a combination of Droplet Measurement Technologies (DMT) electrochemical concentration cell (ECC) ozonesondes and RS-92 radiosondes in 2011; the DMT sonde that was adopted at this site in 2010 is essentially the same instrument as previously supplied by the ENSCI Corporation
Summary
Ground-level ozone is a routinely monitored pollutant in the US, important information about regional and intra- and inter-regional transport comes from measurements of ozone profiles because they encompass the levels in the middle and lower troposphere at which transport occurs. A multi-decadal record of ozone profiles taken by ozonesondes in the US exists for two sites only (Boulder, Colorado, 40 N, 105 W; Wallops Island, Virginia, 37.85 N, 75.5 W). These records have been augmented since the 1990’s at Huntsville, Alabama, typically not in the reach of an urban environment, and Trinidad Head, California, a station downwind of growing Asian emissions (Cooper et al 2011). Since 2004 two urban regions have been sampled with some regularity during their ozone seasons: Houston, Texas, (Morris et al 2006; Morris et al 2010; Rappenglueck et al 2008) and Washington, DC (Thompson et al 2007a; Thompson et al 2007b; Morris et al 2007; Yorks et al 2009). In the case of Washington, DC, these conclusions are consistent with summertime aircraft profiles over Maryland (Taubman et al 2006; Hains et al 2008)
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