Synthetic UV filters: a previously unrecognized atmospheric heating agent

Although atmospheric brown carbon exerts warming effects by absorbing shortwave radiation, its sustainability is limited by photobleaching. In contrast, synthetic ultraviolet (UV) filters can dissipate absorbed UV radiation as thermal energy and retain structural stability. However, their atmospheric heating effects remain poorly understood. We designed a vacuum calorimetric chamber to quantify the heating potential (HP) of synthetic UV filters. The HP of four typical synthetic UV filters was 12–31 W mg −1 , greatly exceeding that of p -coumaric acid (5.39 W mg −1 ), a natural UV filter, and 4-nitrocatechol (6.36 W mg −1 ), a widespread brown carbon chromophore. Unlike p -coumaric acid, which undergoes photobleaching, synthetic UV filters maintain stable HP under UV radiation. Although four synthetic UV filters constituted only 0.02‰–0.35‰ of the total atmospheric organic matter (AOM), they collectively contributed 1.6–39.5‰ to the HP of AOM. Based on global consumption of synthetic UV filters, preliminary projections indicate that Temperate North America, Central Asia, and Boreal North America are key regions highly susceptible to atmospheric heating induced by these chemicals. Synthetic UV filters are non-negligible anthropogenic contributors to atmospheric heating, shedding new light on an unrecognized climate forcing agent.