Climate change: aging of organic aerosols is caused by OH radicals

Science Daily: Atmospheric aerosol particles have a significant effect on climate. An international team of researchers has now discovered that a chemical process in the atmosphere called aging determines to a major extent the concentration and the characteristics of aerosol particles. To date, this aspect has not been accounted for in regional and global climate models. In the Muchachas [Multiple Chamber Aerosol Chemical Aging Experiments] project, the team has not only managed to demonstrate the effects of aging but has also been able to measure these.

...The quality of air is determined to a considerable extent by aerosol particles. In the form of a fine dust, they are believed to be responsible for a series of respiratory diseases and cardiovascular disorders. In addition, aerosol particles also have various effects on atmospheric radiation balance. Aerosols make a direct contribution to radiation levels in the cloud-free atmosphere by dispersing, reflecting, and absorbing sunlight. Aerosols are also essential for cloud formation in the troposphere: They act as condensation nuclei which even in the presence of low levels of water vapor do enable droplets to form.

The size and concentration of aerosol particles is also of great importance for the number of cloud drops, which in turn influences the reflection characteristics of clouds. Hence, aerosol particles tend to have a cooling influence on the atmosphere. However, the precise processes and feedback mechanisms have not yet been fully understood, so that the interaction between aerosol particles, their suitability as cloud condensation nuclei, and the sunlight reflected off Earth's surface represented one of the greatest uncertainties in the calculation of climatic activity.

The Muchachas project looked at organic aerosols, which constitute the largest proportion of chemical airborne particles. Organic aerosols are generated above forests, for example, and they are visible in the form of a blue mist in certain places such as the Great Smoky Mountains, the Blue Ridge Mountains, and the Blue Mountains. In densely populated areas however, anthropogenically generated and released hydrocarbons play an important role as precursor of the development of secondary organic aerosols....

Mist rising from the Blue Ridge Mountains, shot by Jürgen Nagel (Jürgen Nagel), Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license