Compounded extremes in urban environments

Cities are hotter than the surrounding rural areas due to their capacity to retain and redistribute heat throughout the day. The materials that dominate the urban environment are more effective at storing heat than water. This phenomenon is commonly referred to as the urban heat island effect (UHI), and its impact is felt from the surface to the height of the planetary boundary layer (around 10% of the troposphere). During extreme heat episodes, the UHI effect intensifies. In addition to excessive heat, the UHI effect and increased aerodynamic drag affect air quality. The high level of anthropogenic activity in urban areas results in a higher concentration of primary pollutants like nitrogen oxides (NOx), sulfur oxides (SOx), and PM 2.5. Furthermore, these primary pollutants chemically react with other compounds to form secondary pollutants like ozone, all of which are highly detrimental to health. PM2.5 is known to penetrate deep into the lungs and impair lung function. In addition to respiratory illnesses, recent studies have linked PM2.5 to cognitive decline. Ozone, which is produced by the photochemical reaction between water vapor and nitrogen oxides, is also known to cause severe health issues across all age groups. Near-surface ozone leads to both respiratory and cardiovascular illnesses. These pollutants, along with NOx and SOx, are a significant cause for concern in urban areas. Extended exposure to these pollutants could lead to various cancers and early death. The compounded impact of heat and air quality is universally felt in both developed and developing countries. The 2003 European Heatwave caused 70000 casualties; in India, it is estimated that poor air quality leads to 1.5 million excess deaths annually.

Our work addresses this issue in two ways: first, by developing an urban-focused forecast of primary pollutants, and second, by developing targeted strategies to avoid risk exposure in vulnerable populations. Utilizing New York City as our base, our team has developed a state-of-the-art air quality forecasting model that couples urban meteorology with chemistry. Our ongoing work intends to bridge the gap between regional and human scales. To achieve this, we have developed a comprehensive sensor network that monitors both neighborhood and indoor air quality. We are closely working with several vulnerable communities and directly interface with our stakeholders on their every issue with heat and air quality.

Comparing the performance of urbanized WRF CHEM (our model) with current forecasting models, NOAA RAP Chem, and NASA GEOS. The dots represent street-level mobile measurements of PM 2.5 made during the Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas(AEROMMA) campaign. The increased resolution and urban physics help Urban WRF-Chem to better estimate PM2.5 concentration.