Artificial light at night extends pollen season and elevates allergen exposure.

Artificial light at night (ALAN), a growing environmental stressor in urban ecosystems, disrupts natural light-dark cycles and alters plant phenological events such as leaf-out and flowering. However, the extent to which ALAN influences airborne pollen season timing and exacerbates allergy-related health risks remains largely understudied. This study investigates how ALAN influences the timing and duration of the airborne pollen season across the Northeastern United States from 2012 to 2023 and the consequences of allergenic pollen exposure. Using daily pollen concentrations from the National Allergy Bureau, ALAN data from the Visible Infrared Imaging Radiometer Suite product, and gridded Daymet climate data, we derived three key pollen season metrics: start of season, end of season, and season length, and examined their relationship with environmental conditions. We found that higher ALAN exposure was significantly associated with an earlier start of pollen season, a later end of season, and a longer pollen season length, after controlling for temperature and precipitation. ALAN's impact on the end of the season is larger than on the start of the season. ALAN sites experienced more days and higher severity for allergenic pollen exposure, relative to sites with minimal or no ALAN exposure. These results underscore the potential of ALAN to exacerbate allergy-related disease burdens, calling for its integration into urban environmental public health and planning strategies.