Study shows that organic aerosols aging caused by OH radicals

Oct 05, 2012
Processes investigated in the MUCHACHAS Project

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. Their findings have been published in the specialist journal Proceedings of the National Academy of Sciences (PNAS).

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 and cardiovascular disorders. In addition, aerosol particles also have various effects on atmospheric . Aerosols make a direct contribution to in the cloud-free atmosphere by dispersing, reflecting, and absorbing sunlight. Aerosols are also essential for in the troposphere: They act as condensation nuclei which even in the presence of low levels of water vapor do enable droplets to form.

Online aerosol mass spectrometer in a measurement container during an analytical run. ©: AG Hoffmann

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 the earth's surface represented one of the greatest uncertainties in the calculation of climatic activity.

The Muchachas project looked at , 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.

The experiments showed that the mass and composition of organic aerosols are significantly influenced by OH radicals. OH radicals are the most important oxidants in the atmosphere and make an important contribution to keeping air clean. Researchers from Pittsburgh (USA), Juelich, Karlsruhe, and Mainz (Germany), Gothenburg (Sweden), Copenhagen (Denkmark), and Villigen (Switzerland) analyzed results in four different, large-volume atmospheric simulation chambers and found that the oxidation process called chemical aging has a significant impact and influence on the characteristics and concentration of organic aerosols over their entire life cycle.

"New climate models will have to take these findings into account," says Professor Dr. Thorsten Hoffmann of the Institute of Inorganic Chemistry and Analytical Chemistry at Johannes Gutenberg University Mainz (JGU) in Germany. The Mainz researchers contributed primarily to the development of analytical techniques for studying the chemical composition of the aerosol particles in the Muchachas project. Thanks to their development of so-called 'soft ionization' techniques and the corresponding mass spectrometers, Hoffmann's work group was able to track the concentration of individual molecule species in the atmospheric simulation chamber and thus observe the chemical aging of the atmospheric aerosols at the molecular level. It was clearly demonstrated that oxidation occurred in the gaseous phase and not in the particle phase. "Now the goal is to integrate these underlying reactions in models of regional and global atmospheric chemistry and so reduce the discrepancy between the expected and the actually observed concentrations of organic aerosol particles," explains Hoffmann.

Explore further: Better forecasts for sea ice under climate change

More information: Donahue et al., "Aging of biogenic secondary organic aerosol via gas-phase OH radical reactions", Proceedings of the National Academy of Sciences (PNAS), 21 August 2012 doi:10.1073/pnas.1115186109

add to favorites email to friend print save as pdf

Related Stories

Airborne Mites

Nov 24, 2005

Aerosol particles influence atmospheric chemistry, climate, and human health They are tiny and very finely dispersed and play important roles for our climate and health. We are talking about aerosol particles, airborne droplets ...

Tiny particles, big impact

Jun 03, 2011

Atmospheric aerosols may be small, ranging in size from a few nanometers to a few microns, but they have a big impact on climate.  At the Pacific Northwest National Laboratory, capabilities developed ...

Size Matters: From Aerosol Particles to Cloud Droplets

Jun 02, 2006

Clouds play a central role in the Earth’s climate system and water cycle. A cloud’s behavior depends to a great extent on the number and size of the droplets it is made of. Since each of these droplets ...

Scientists study how water condenses to form clouds

Jul 02, 2012

Researchers at the University of Bristol with collaborators from ETH-Zurich have shown that the rate of condensation of water on organic aerosol particles in the atmosphere can be very slow, taking many hours ...

Sunlight changes aerosols in clouds

Oct 12, 2011

(PhysOrg.com) -- Today's climate models regard organic aerosols as static carbon-based molecules, but scientists at Pacific Northwest National Laboratory and the University of California, Irvine showed that ...

Recommended for you

Better forecasts for sea ice under climate change

12 hours ago

University of Adelaide-led research will help pinpoint the impact of waves on sea ice, which is vulnerable to climate change, particularly in the Arctic where it is rapidly retreating.

"Ferrari of space' yields best map of ocean currents

21 hours ago

A satellite dubbed the "Ferrari of space" has yielded the most accurate model of ocean circulation yet, boosting understanding of the seas and a key impact of global warming, scientists said Tuesday.

Researcher studies deformation of tectonic plates

23 hours ago

Sean Bemis put his hands together side by side to demonstrate two plates of the earth's crust with a smooth boundary running between them. But that boundary is not always smooth and those plates do not always ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.