Phoenix Regional Heat and Air Quality Knowledge Repository

Public transit systems have been identified as a critical component to reducing energy use and greenhouse gas emissions associated with the transportation sector to mitigate future climate change impacts. A unique aspect of public transit is its use almost always necessitates environmental exposure and the design of these systems directly influences rider exposure via rider ingress, egress, and waiting. There is a tension between policies and programs which promote transit use to combat climate change and the potential impact an uncertain climate future may have on transit riders.

In the American Southwest, extreme heat events, a known public health threat, are projected to increase between 150 and 840% over the next decade, and may be a health hazard for transit riders. There are opportunities to incorporate rider health risks in the overall planning process and develop alternative transit schedules during extreme heat events to minimize these risks. Using Los Angeles Metro as a case studies, we show that existing transit vehicles can be reallocated across the system to significantly reduce exposure for riders who are more vulnerable to heat while maintaining a minimum level of service across the system. As cities continue to invest in public transit it is critical for them to understand transit use as an exposure pathway for riders and to develop strategies to mitigate potential health risks.

A web-based software tool has been developed to assist urban planners and air quality management officials in assessing the potential ofurban heat island mitigation strategies to affect the urban climate, air quality, and energy consumption within their cities. The user of thetool can select from over 170 US cities for which to conduct the analysis, and can specify city-wide changes in surface reflectivity and/or veg-etative cover. The Mitigation Impact Screening Tool (MIST) then extrapolates results from a suite of simulations for 20 cities to estimate airtemperature changes associated with the specified changes in surface characteristics for the selected city. Alternatively the user can simply definea nominal air temperature reduction that they hope to achieve with an unspecified mitigation scenario. These air temperature changes are theninput to energy and ozone models to estimate the impact that the mitigation action may have on the selected city. The results presented by MISTinclude a high degree of uncertainty and are intended only as a first-order estimate that urban planners can use to assess the viability of heatisland mitigation strategies for their cities. As appropriate, MIST analyses should be supplemented by more detailed modeling.

Urban green space is purported to offset greenhouse‐gas (GHG) emissions, remove air and water pollutants, cool local climate, and improve public health. To use these services, municipalities have focused efforts on designing and implementing ecosystem‐services‐based “green infrastructure” in urban environments. In some cases the environmental benefits of this infrastructure have been well documented, but they are often unclear, unquantified, and/or outweighed by potential costs. Quantifying biogeochemical processes in urban green infrastructure can improve our understanding of urban ecosystem services and disservices (negative or unintended consequences) resulting from designed urban green spaces. Here we propose a framework to integrate biogeochemical processes into designing, implementing, and evaluating the net effectiveness of green infrastructure, and provide examples for GHG mitigation, stormwater runoff mitigation, and improvements in air quality and health.