Jonathan Williams

The 2026 Vilhelm Bjerknes Medal is awarded to Jonathan Williams for leading, significant and sustained contributions to our understanding of volatile organic compounds, in the outdoor and indoor atmosphere.

Jonathan Williams is an established international leader in biogenic volatile organic compounds (BVOCs) and their impact on atmospheric chemistry, indoor air quality and climate. He has made numerous important discoveries that have grown our understanding of how BVOCs are emitted from, and modified by ecosystem-atmosphere interactions. He has carried out extensive work over the Amazon rainforest, the largest source of BVOC in the atmosphere. He has shown that tropical forest soils are strong, previously unaccounted for sources highly reactive BVOCs that readily form secondary aerosols and, through deep convection can influence the chemistry of the upper troposphere as well as the tropical forest atmosphere. He has also led the way in innovative instrument design and deployment, being an early champion of proton transfer mass spectrometry (PTR MS) for fast in situ volatile organic compound (VOC) measurements, demonstrating its utility for atmospheric chemistry measurements; methods that have now become the gold standard.  He proposed and developed a method to directly measure the total reactivity of an air mass with respect to the most important tropospheric oxidant, the hydroxyl radical (OH), which has allowed an assessment of the fraction of the OH reactive species that are captured by current measurements.  This approach has subsequently been widely applied internationally.  Through a series of innovative experiments, he has demonstrated that people generate OH in the presence of ozone via the ozonolysis of skin-emitted alkenes. Up to that point, is had been assumed that ozone reactions dominate organic compound oxidation in the indoor environment, but his team showed that the OH radicals generated by the so-called “human oxidation field” are sufficiently high to outcompete ozonolysis.  This novel and surprising finding has implications for indoor air quality and for human health.  
 
In summary, Jonathan Williams is awarded the Vilhelm Bjerknes Medal of the EGU for his leading, significant and sustained contributions to the understanding of volatile organic compounds in the outdoor and indoor atmosphere. His scientific curiosity and innovation are an inspiration to others.