A recent paper by Pfannerstil highlights the potential of airborne eddy flux measurements (Temperature-dependent emissions dominate aerosol and ozone formation in Los Angeles | Science). They show that up to 60% of the VOC reactivity is associated with biogenic emissions. Despite the great strides that have been made in reducing urban pollution in major North America and European cities, there is much that remains unclear about the causes of such pollution. Mapping urban haze | Science