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Abstract Climate change, urbanization, and economic growth are expected to drive increases in the installation of new air conditioners, as well as increases in utilization of existing air conditioning (AC) units, in the coming decades. This growth will provide challenges for a diversity of stakeholders, from grid operators charged with maintaining a reliable and cost-effective power system, to low-income communities that may struggle to afford increased electricity costs. Despite the importance of building a quantitative understanding of trends in existing and future AC usage, methods to estimate AC penetration with high spatial and temporal resolution are lacking. In this study we develop a new classification method to characterize AC penetration patterns with unprecedented spatiotemporal resolution (i.e. at the census tract level), using the Greater Los Angeles Area as a case study. The method utilizes smart meter data records from 180 476 households over two years, along with local ambient temperature records. When spatially aggregated, the overall AC penetration rate of the Greater Los Angeles Area is 69%, which is similar to values reported by previous studies. We believe this method can be applied to other regions of the world where household smart meter data are available. 

Abstract. Parameterizations that impact wet removal of black carbon (BC)remain uncertain in global climate models. In this study, we enhance thedefault wet deposition scheme for BC in the Community Earth System Model (CESM)to (a) add relevant physical processes that were not resolved in thedefault model and (b) facilitate understanding of the relative importanceof various cloud processes on BC distributions. We find that the enhancedscheme greatly improves model performance against HIPPO observationsrelative to the default scheme. We find that convection scavenging, aerosolactivation, ice nucleation, evaporation of rain or snow, and below-cloudscavenging dominate wet deposition of BC. BC conversion rates for processesrelated to in-cloud water–ice conversion (i.e., riming, the Bergeronprocess, and evaporation of cloud water sedimentation) are relativelysmaller, but have large seasonal variations. We also conduct sensitivitysimulations that turn off each cloud process one at a time to quantify theinfluence of cloud processes on BC distributions and radiative forcing.Convective scavenging is found to have the largest impact onBC concentrations at mid-altitudes over the tropics and even globally. Inaddition, BC is sensitive to all cloud processes over the NorthernHemisphere at high latitudes. As for BC vertical distributions, convectivescavenging greatly influences BC fractions at different altitudes.Suppressing BC droplet activation in clouds mainly decreases the fraction ofcolumn BC below 5 km, whereas suppressing BC ice nucleation increases thatabove 10 km. During wintertime, the Bergeron process also significantlyincreases BC concentrations at lower altitudes over the Arctic. Oursimulation yields a global BC burden of 85 Gg; corresponding directradiative forcing (DRF) of BC estimated using the Parallel Offline RadiativeTransfer (PORT) is 0.13 W m−2, much lower than previous studies. Therange of DRF derived from sensitivity simulations is large, 0.09–0.33 W m−2,corresponding to BC burdens varying from 73 to 151 Gg. Due todifferences in BC vertical distributions among each sensitivity simulation,fractional changes in DRF (relative to the baseline simulation) are alwayshigher than fractional changes in BC burdens; this occurs because relocating BCin the vertical influences the radiative forcing per BC mass. Our resultshighlight the influences of cloud microphysical processes on BC concentrationsand radiative forcing. 

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. 

Urban greenery is a natural solution to cool cities and provide comfort, clean air and significant social, health and economic benefits. This paper aims to present the latest progress on the field of greenery urban mitigation techniques including aspects related to the theoretical and experimental assessment of the greenery cooling potential, the impact on urban vegetation on energy, health and comfort and the acquired knowledge on the best integration of the various types of greenery in the urban frame. Also to present the recent knowledge on the impact of climate change on the cooling performance of urban vegetation and investigate and analyse possible technological solutions to face the impact of high ambient temperatures. 

The effects of neighborhood-scale land use and land cover (LULC) properties on observed air temperatures are investigated in two regions within Los Angeles County: Central Los Angeles and the San Fernando Valley (SFV). LULC properties of particular interest in this study are albedo and tree fraction. High spatial density meteorological observations are obtained from 76 personal weather-stations. Observed air temperatures were then related to the spatial mean of each LULC parameter within a 500 m radius “neighborhood” of each weather station, using robust regression for each hour of July 2015. For the neighborhoods under investigation, increases in roof albedo are associated with decreases in air temperature, with the strongest sensitivities occurring in the afternoon. Air temperatures at 14:00–15:00 local daylight time are reduced by 0.31 °C and 0.49 °C per 1 MW increase in daily average solar power reflected from roofs per neighborhood in SFV and Central Los Angeles, respectively. Per 0.10 increase in neighborhood average albedo, daily average air temperatures were reduced by 0.25 °C and 1.84 °C. While roof albedo effects on air temperature seem to exceed tree fraction effects during the day in these two regions, increases in tree fraction are associated with reduced air temperatures at night.