Ozone Variability and Anomalies Observed During SENEX and SEAC⁴RS Campaigns in 2013

Abstract

Tropospheric ozone variability occurs because of multiple forcing factors including surface emission of ozone precursors, stratosphere‐to‐troposphere transport (STT), and meteorological conditions. Analyses of ozonesonde observations made in Huntsville, AL, during the peak ozone season (May to September) in 2013 indicate that ozone in the planetary boundary layer was significantly lower than the climatological average, especially in July and August when the Southeastern United States (SEUS) experienced unusually cool and wet weather. Because of a large influence of the lower stratosphere, however, upper tropospheric ozone was mostly higher than climatology, especially from May to July. Tropospheric ozone anomalies were strongly anticorrelated (or correlated) with water vapor (or temperature) anomalies with a correlation coefficient mostly about 0.6 throughout the entire troposphere. The regression slopes between ozone and temperature anomalies for surface up to midtroposphere are within 3.0–4.1 ppbv K−1. The occurrence rates of tropospheric ozone laminae due to STT are ≥50% in May and June and about 30% in July, August, and September suggesting that the stratospheric influence on free‐tropospheric ozone could be significant during early summer. These STT laminae have a mean maximum ozone enhancement over the climatology of 52 ± 33% (35 ± 24 ppbv) with a mean minimum relative humidity of 2.3 ± 1.7%.

Influence of Cold Fronts on Variability of Daily Surface O3 over the Houston-Galveston-Brazoria Area in Texas USA during 2003–2016

“…It is consistent with the O 3 -RH correlation that transitioning from positive to negative south of 37 • N [39]. The O 3 /RH regression slopes in Huntsville, AL, during the peak O 3 season (May to September) in 2013 were −1.0, −0.6, −0.5, and −3.6 ppb/% for the surface, PBL, mid-troposphere, and upper troposphere, respectively [41]. O 3 anomalies (deviation from normal value) reached +12 ppb from 30 to 36 • N in 1999, and 4-7 ppb higher, during the historic 2007 drought in the Southeastern United States (U.S.) [39,42].…”

“…O 3 was at first removed efficiently by chemical reactions then increased rapidly when warmer and O 3 -richer air from aloft was mixed downward to the surface. Leibensperger et al [6] reported that the frequency of summertime mid-latitude cyclones (and their associated cold fronts) tracking across eastern North America at [40][41][42][43][44][45][46][47][48][49][50] • N is a strong predictor of stagnation and O 3 pollution days in the eastern US.…”

Taehwa Research Forest: a receptor site for severe domestic pollution events in Korea during 2016

“…Within the free troposphere from 2 to 6 km, median and lower quartile O 3 values were from 73 to 81 and 66 to 74 ppbv, respectively. This is markedly larger than the 50-65 ppbv baseline O 3 estimates derived for Trinidad Head, CA; Boulder, CO; and Huntsville, AL, USA (Stauffer et al, 2016;Kuang et al, 2017). This highlights the infrequency (i.e., < 25 % of the time) of measuring less than 66 ppbv of O 3 within the boundary layer and free troposphere and the subsequent regulatory challenge of meeting the 8 h Korean O 3 standard (60 ppbv).…”

Very high stratospheric influence observed in the free troposphere over the Northern Alps – just a local phenomenon?

“…The results obtained from the sondes have been rather controversial which seems to be the consequence of the individual data-filtering approach. Recent sonde studies confirm a rather high percentage of STT: At the same latitude as Table Mountain, but in the south-eastern United States, ozone-sonde measurements at Huntsville (Alabama, U.S.A., 35º N) were analysed between May and September 2013 (Kuang et al, 2017). There, the summer minimum was 23 % (August), and 50-60 % were reached in May-20 June.…”

“…STT analyses have also been derived from ozone-sonde data (e.g., Beekmann et al, 1997;Colette and Ancellet, 2005;Kuang et al, 2017;Tarasick et al, 2019). Ozone sondes yield a substantially lower temporal data coverage than lidar sounding.…”