The influence of the SAL and lightning on tropospheric ozone variability over the Northern Tropical Atlantic: Results from Cape Verde during 2010

Abstract

[1] We present results for multiple Saharan Air Layer (SAL) events and their relationship to tropospheric ozone mixing ratios that were observed in the Eastern Atlantic during the summer of 2010 using ozonesondes. In particular, 5 SAL events are sampled during 2010 in Cape Verde indicting a reduction of ozone mixing ratios throughout much of the SAL layer, except near the base of the SAL. In this layer of enhanced ozone mixing ratio, we find increases of 20-30 ppb in some cases between non-SAL and SAL conditions. In addition, ozone concentrations are enhanced above the SAL layer, with trajectories suggesting enhancements by lightning from the middle/upper troposphere with outflow from Africa. Additional aircraft measurements are required to examine the chemical and aerosol distributions from the Marine Boundary Layer (MBL) through the upper troposphere to determine the heterogeneous chemical processes related to reduced ozone mixing ratio, and further quantify elevated ozone mixing ratios at the base of the SAL and above the SAL.

Atmospheric boundary layer and ozone-aerosol interactions under Saharan intrusions observed during AMISOC summer campaign

“…Lower surface ozone concentrations, therefore, would be expected during DD conditions (Jenkins et al, 2012a;De Reus et al, 2005). The results, however, do not agree with that idea.…”

The seasonal vertical distribution of the Saharan Air Layer and its modulation by the wind

“…In addition, Saharan dust may serve as cloud condensation nuclei or ice nuclei, affecting cloud microphysics and decreasing precipitation Mahowald and Kiehl, 2003;Twohy et al, 2009). During dust events, the concentration of trace gases -like ozone, nitrogen oxides and organic radicals -is reduced due to heterogeneous reactions on dust aerosols (de Reus et al, 2005;Jenkins et al, 2012), thus changing the oxidizing capacity of the atmosphere. Besides, SAL dust aerosols fertilize large areas of the Atlantic Ocean and Amazon Basin by transport and deposition of micronutrients, like iron and phosphorus, which in turn may impact many biogeochemical cycles (Jickells et al, 2005;Kaufman et al, 2005;Bristow et al, 2010).…”

WRF-Chem model estimates of equatorial Atlantic Ocean tropospheric ozone increases via June 2006 African biomass burning ozone precursor transport

“…3) is related to biomass burning. Even though we have quantified the biomass burning emission contribution here, observations of high ozone mixing ratios in the MT and UT in the SH, specifically at Ascension Island, over the Equatorial Atlantic Ocean (Morris et al 2006;Hawkins 2007;Jenkins et al 2008;Nalli et al 2011;Smith 2012) and in the Sahel of NH Africa (Jenkins et al 2012; are not fully explained from biomass burning alone. Other tropospheric ozone sources exist in the eastern Equatorial Atlantic Ocean (i.e.…”

“…The model predicts synoptic and mesoscale meteorological features that affect the horizontal and vertical transport of chemical constituents and aerosols. The WRFChem model is suitable for simulations in the tropical latitudes (see Jenkins et al 2012;Zhang and Chen 2012). Hence, this study uses two simulations to make conclusions specifically for June 2006: 1) a simulation without biomass burning emissions called a control simulation and 2) and one with biomass burning emissions (BB simulation) at 20 km grid spacing.…”