Abstract

International audience; The High Altitude Ice Crystals (HAIC) Sub-Project 3 (SP3) focuses on the detection of cloud regions with high ice water content (IWC) from current available remote sensing observations of space-based geostationary and low-orbit missions. The SP3 activities are aimed at supporting operationally the two up-coming HAIC flight campaigns (the first one in May 2015 in Cayenne, French Guyana; the second one in January 2016 in Darwin, Australia) and ultimately provide near real-time cloud monitoring to Air Traffic Management. More in detail the SP3 activities focus on the detection of high IWC from space-borne geostationary Meteosat daytime imagery, explore the synergy of concurrent multi-spectral multiple-technique observations from the low-orbit A-Train mission to identify specific signatures in high IWC cloud regions, and finally develop a satellite-based nowcasting tool to track and monitor convective systems over the Tropical Atlantic. The paper presents the HAIC SP3 objectives and provides an objective status of the sub-project at mid term of the HAIC project.

Abstract

The lockdown measures implemented worldwide to slow the spread of the COVID–19 pandemic have allowed for a unique real–world experiment, regarding the impacts of drastic emission cutbacks on urban air quality. In this study we assess the effects of a 7–week (23 March–10 May, 2020) lockdown in the Greater Area of Athens, coupling in situ observations with estimations from a meteorology–atmospheric chemistry model. Measurements in central Athens during the lockdown were compared with levels during the pre– and post–lockdown 3–week periods and with respective levels in the four previous years. We examined regulatory pollutants as well as CO"sub"2"/sub", black carbon (BC) and source–specific BC components. Models were run for pre–lockdown and lockdown periods, under baseline and reduced–emissions scenarios. The in–situ results indicate mean concentration reductions of 30–35% for traffic–related pollutants in Athens (NO"sub"2"/sub", CO, BC from fossil fuel combustion), compared to the pre–lockdown period. A large reduction (53%) was observed also for the urban CO"sub"2"/sub" enhancement while the reduction for PM"sub"2.5"/sub" was subtler (18%). Significant reductions were also observed when comparing the 2020 lockdown period with past years. However, levels rebounded immediately following the lift of the general lockdown. The decrease in measured NO"sub"2"/sub" concentrations was reproduced by the implementation of the city scale model, under a realistic reduced–emissions scenario for the lockdown period, anchored at a 46% decline of road transport activity. The model permitted the assessment of air quality improvements on a spatial scale, indicating that NO"sub"2"/sub" mean concentration reductions in areas of the Athens basin reached up to 50%. The findings suggest a potential for local traffic management strategies to reduce ambient exposure and to minimize exceedances of air quality standards for primary pollutants. Document type: Article