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Municipalities often consider heat mitigation strategies to address urban overheating, but the location of implementation rarely is co-located with the communities that are carrying the majority of the heat burden in the city. The City of Phoenix, is redeveloping a public housing community with a focus on urban cooling as a desired outcome. This research uses in situ measurements (including the mobile micro-meteorological measurement cart, MaRTy) and ENVI-met microscale modeling of the neighborhood to assess air temperature (Tair) cooling capabilities of the planned redesigns to the neighborhood. After validating the ENVI-met model of the current neighborhood with fixed and mobile measurements with an index of agreement d > 0.9 and d > 0.8, respectively, analysis of the planned urban design shows some cool spots connected to new shade and vegetated corridors with Tair cooling magnitudes as high as 3 °C. Yet, some exposed and building-adjacent areas were identified as potential hot spots in the planned neighborhood. These hotspots underscore the importance of continued collaboration among the City, researchers, and the community to address the needs of the community for the creation of healthier urban environments. 

Abstract. Urbanization has a profound influence on regional meteorology and air qualityin megapolitan Southern California. The influence of urbanization onmeteorology is driven by changes in land surface physical properties and landsurface processes. These changes in meteorology in turn influence air qualityby changing temperature-dependent chemical reactions and emissions,gas–particle phase partitioning, and ventilation of pollutants. In this studywe characterize the influence of land surface changes via historicalurbanization from before human settlement to the present day on meteorology andair quality in Southern California using the Weather Research and ForecastingModel coupled to chemistry and the single-layer urban canopy model(WRF–UCM–Chem). We assume identical anthropogenic emissions for thesimulations carried out and thus focus on the effect of changes in landsurface physical properties and land surface processes on air quality.Historical urbanization has led to daytime air temperature decreases of up to1.4 K and evening temperature increases of up to 1.7 K. Ventilation of airin the LA basin has decreased up to 36.6 % during daytime and increasedup to 27.0 % during nighttime. These changes in meteorology are mainlyattributable to higher evaporative fluxes and thermal inertia of soil fromirrigation and increased surface roughness and thermal inertia frombuildings. Changes in ventilation drive changes in hourlyNOx concentrations with increases of up to 2.7 ppb duringdaytime and decreases of up to 4.7 ppb at night. Hourly O3concentrations decrease by up to 0.94 ppb in the morning and increase by upto 5.6 ppb at other times of day. Changes in O3 concentrations aredriven by the competing effects of changes in ventilation and precursorNOx concentrations. PM2.5 concentrations show slightincreases during the day and decreases of up to 2.5 µg m−3at night. Process drivers for changes in PM2.5 include modificationsto atmospheric ventilation and temperature, which impact gas–particle phasepartitioning for semi-volatile compounds and chemical reactions.Understanding process drivers related to how land surface changes effectregional meteorology and air quality is crucial for decision-making on urbanplanning in megapolitan Southern California to achieve regional climateadaptation and air quality improvements.