Connection among meteorological observations,columnar aerosol properties and urban heat island during nighttime extreme heat events in the uRban hEat and pollution iSlands inTerAction in Rome and possible miTigation strategies(RESTART)project

The “uRban hEat and pollution iSlands inTerAction in Rome and possible miTigation strategies” (RESTART) is a 2-years project, funded by the Italian Ministry for University and Research as a Project of National Interest (PRIN2022).RESTART aims to explore the interaction between the Urban Heat Island (UHI) and the Urban Pollution Island (UPI) in Rome (Italy),providing a series of mitigation strategies, including tailored Nature-Based Solutions, and ready-to-use guidelines for the improvement of well-being and liveability in urban environments. The connection between UHI and UPI is investigated by inspecting quality-checked datasets of meteorological trace gases and aerosol observations, provided by local and international observatories and dense networks of instruments in Rome.Specifically,the UHI is studied by examining the time series of atmospheric near-surface temperature (average, minimum, maximum daily), relative humidity, pressure, and wind speed, while the UPI is characterised by the observations of trace gases (e.g., NO, NO2, O3, CO), particulate matter (PM10, PM2.5),aerosols optical properties (e.g., aerosol optical depth, AOD, Ångström exponent, single scattering albedo, SSA, particle volume size distribution) in terms of surface and columnar contents and vertical profiles, based on the availability of measurements.The city of Rome (Lat. 41.90 °N, Lon. 12.54 °E) is the most populous and extended Italian city and the third most densely populated metropolis in Europe. Rome is located in the central region of the Italian Peninsula, about 27 km inland from the Tyrrhenian coast. Due to its position in the middle of the Mediterranean Basin and the complex orography of its surroundings, the city is frequently subjected to the advection of Saharan dust in the case of persistent southerly winds, and to the sea breeze regime from the southwest, the latter particularly evident during summertime under anticyclonic conditions. In recent years, the city has experienced significant atmospheric warming and a substantial intensification of extreme weather events, such as heat waves, tropical nights, and droughts.This work explores the connection among some meteorological observations (near-surface temperature and relative humidity) from weather stations, columnar aerosol properties (AOD and SSA) from Skynet and AERONET international networks, and UHI intensities during heat waves, paying particular attention to nighttime. During the selected events, the synoptic weather conditions affecting the interaction between the UHI and the aerosol properties, are discussed.