Back-Trajectory Analysis of Ozone Concentrations in the Lower, Middle and Upper Troposphere during the LASIC 2017 Field Campaign

The presence of tropospheric ozone and consequently understanding its horizontal and vertical spatial distribution is important. Ozone acts as a source of tropospheric warming. During the late summer, the ozone values tend to increase and reach its peak in the months of SON. During the summer of 2017, twenty (20) ozonesondes were launched during the period of August 17 – October 5^th. We use HYSPLIT backward trajectories to determine the sources of high and low ozone concentrations during the period. Trajectories are grouped into the lower troposphere (surface – 850hpa), middle troposphere (850 – 535hPa) and upper troposphere (475 – 325hPa) and undertaken for individual ozonesondes. Our results show that high ozone mixing ratios in the middle troposphere came primarily from Central Africa via biomass burning while elevated levels in the upper troposphere that may have been produced by lightning (LNOX) also emerged from Central Africa. Low ozone episodes typically came from the South Atlantic but individual cases also show that the lowest observed ozone emerged from the Northern Tropical Atlantic just off the coast of West Africa. September 15, 2017, show two distinct contributions to the vertical profiles of ozone: Central Africa (>700hPa) and South America (<700hPa). We present these cases and provide a total estimate for the full campaign. In August 18, September 8 and September 15, the ozone values are low. However, during October 2, the highest ozone values were found between 800 – 600hPa. Several observations confirm that the marine boundary is clean between surface to 900hPa, in 800 – 300hPa the ozone mixing ratios are the highest. In addition, when AOD are higher the ozone mixing ratios are high too. Westerly winds are not commonly found it near the surface, because the easterly winds dominate this layer for most of the year. However, August 17-19, September 8 and 15 shows westerly flow in this layer. After as well analyzing HYSPLIT backward trajectories until September 8, we registered an unusual low ozone peak, and observed that air pollution came from the South Atlantic near to Western Africa. Furthermore, when looked of the days where we registered very high ozone levels, they came from Central Africa and were related with the biomass burning. In addition, this air is moved by easterly wind to Ascension Island, and because of the convection process, this air came from high altitude in the troposphere. Likewise, the wet season in the Southern Hemisphere is characterized by lightning development over Africa and the same time an enhance tropospheric column ozone values across the Southern Atlantic Ocean. The lightning development and enhance TCO were confirmed by the space-borne lightning sensor. During ASO most of the ozone peaks were detected in the upper troposphere came from at a similar altitude were found. Furthermore, those ozone peaks were found in the upper troposphere came from over Africa and South America, and this can be related to the lightning events over those two countries.