Ambient Air Quality: Trees Could Help… <i>but What Goes With the Trees?</i> Reflections, Future Challenges, Potential Opportunities

ABSTRACT The beneficiary roles of trees as natural air purifiers have been known for a long time, that goes into sustainability planning (e.g., health and well‐being , UN‐SDG 3; resilient cities and communities , UN‐SDG 11; life on land , UN‐SDG 15). In this reflective article, however, we ask: Trees Help, But What Goes With The Trees? In other words, trees can intercept, capture, and remove a variety of airborne pollutants, but how does that impact the trees? We scan the world literature ( N = 89) to summarize our experience about two pollutants: particulate matter (PM 2.5 , PM 10 ) and ozone (O 3 ). While we reflect on our state of knowledge about plant‐pollutant interactions, we also highlight the gaps in our current understanding that call for more research. In the process, we highlight changes in various biomolecules (e.g., reactive oxygen species (ROS), proline, and soluble sugars) that accumulate/deplete within plant cells in response to pollutant stress. In the final part of the narrative, we reflect on how our understanding of plant stress could be put to better use—for example, strategic use of plants in sustainable urban planning and development. Here, we discuss current practices around two of the most widely used indicator variables to assess plant stress—air pollution tolerance index (APTI) and anticipated pollution index (API). As we reflect on the significance of each, we discuss the world experience around “tolerant” and “sensitive” species, with the latter being used as air quality biomonitors . For urban applications (tree‐mediated pollutant removal), we emphasize the need to understand the characteristics of the target environment (e.g., street canyon vs. open road; local wind speed and direction) to decide on specific leaf traits, road‐side planting patterns. Overall, we envision more process‐level research to unravel the context‐specific plant‐pollutant interaction pathways (e.g., by different built environment types, local meteorological conditions, and pollutant sources) for the concerned urban authorities to use the information more strategically in developing efficient pollution control interventions.