Lower/middle tropospheric ozone variability in Senegal during pre-monsoon and monsoon periods of summer 2008: observations and model results

Evidence of a LNOX influence on middle/upper troposphere ozone‐mixing ratios at Dakar, Senegal during Northern Hemisphere summer season

“…A steady moistening of the low troposphere (1000-700 hPa) to MT (700-400 hPa) occurs with relative humidity increasing from 30% at 900 hPa in June to 75% during September. The low values of relative humidity during June in the LT are representative of the SAL, which was reported in Jenkins et al (2013b). Above 500 hPa, a drier atmosphere is found during all months.…”

“…The distribution of lightning during 2010 upstream of Dakar, Senegal each month makes LNO X a likely source of enhanced O 3 mixing ratios in the MT/UT (see Supporting Information). During June and July, higher ozone-mixing ratios (>40 ppb) can occasionally be found in the LT, which we have linked to SAL events and potential NO soil emissions (Jenkins et al, 2013b), but in August and September, ozone-mixing ratios are less than 40 ppb from the surface through 700 hPa under more humid conditions. A similar pattern of higher MT/UT ozone-mixing ratios is found at Cape Verde during June and July 2010 (Jenkins et al, 2012).…”

“…Ozone-mixing ratios, however, increase from approximately 20-30 ppb near the surface to 50-60 ppb in the MT/UT. Further, lower ozone-mixing ratios are found from the surface to 700 hPa during August and September in comparison to June/July, which Jenkins et al (2013b) associate with increases in dry and wet deposition once the wet season commences. Increased onshore flow from the Atlantic during August/September may also reduce ozone-mixing ratios in the planetary boundary layer over Dakar because of ozone destruction by Halogens (Read et al, 2008).…”

“…Ozonesonde measurements at Dakar, Senegal (14.49 • N, 17.49 • W) are presented for 4 years (2008, 2010, 2011 and 2012) during the period of June, July, August, September and October. The measurements and procedures for the ozonesondes measurements are found in Jenkins et al (2013a) and(2013b). Table I shows the dates of the measurements by month.…”

“…In this work, we present 4 years of ozone measurements (40 ozone profiles) from the Sahel at a continental outflow site (Dakar, Senegal) where previous ozone measurements are extremely limited (Grant et al, 2008). In recent work, we have focused on ozone measurements in the LT during the wet season (Jenkins et al, 2013b). We have also compared ozone measurements in the Western Atlantic, Eastern Atlantic and continental outflow sites during JJAS of 2010 (Jenkins et al, 2013a).…”