Report
Teaser, summary, work performed and final results
Periodic Reporting for period 3 - COALA (Comprehensive molecular characterization of secondary organic aerosol formation in the atmosphere)
Teaser
Particulate matter in Earth\'s atmosphere impacts society in many ways. It is a pollutant known to be the main cause a variety of detrimental health effects, causing millions of premature deaths each year. In addition, airborne aerosol particles strongly impact the radiation...
Summary
Particulate matter in Earth\'s atmosphere impacts society in many ways. It is a pollutant known to be the main cause a variety of detrimental health effects, causing millions of premature deaths each year. In addition, airborne aerosol particles strongly impact the radiation balance of our planet: they can scatter sun light back into space or impact cloud properties and lifetimes. A large source of uncertainty in the anthropogenic influence on climate comes from the lack of understanding of aerosol particle formation, evolution and fate in the atmosphere. This is what the COALA project targets.
Within COALA, the role of organic emissions on aerosol formation will be quantified comprehensively using mass spectrometric techniques. The volatile emissions are oxidized in the atmosphere to produce vapors of various volatilities. The least volatile will condense and form aerosol, but the fraction of products able to do this (for a given molecule) has been hard to determine, in part due to a lack of methods for quantification of these molecules. The main objectives in COALA are to experimentally detect as large fraction as possible of the oxidation products from the most commonly emitted precursors in the atmosphere, and to utilize this data to map out a volatility distribution of the formed vapors. With this information, we can evaluate how much of the organic aerosol is formed directly through condensation and whether additional chemistry occurring on the surface or inside the particles will influence the amount of organics.
Constraints on the chemical and physical processes leading to organic aerosol formation will directly translate into better constraints on atmospheric models studying the influence of human activity on climate change.
Work performed
During the first half of the project, much effort has been put into designing appropriate laboratory facilities to study the chemistry of emission oxidation under controlled chamber conditions. First experiments have already been conducted and are nearing the publication stage.
From other studies together with our collaborators, several important findings have already been achieved. For example, we have continued to characterize the complex gas phase chemistry of VOC oxidation in different systems, including chamber oxidation of biogenic and anthropogenic precursors, ambient studies as well as computational work. The general indication has been that a large fraction of the organic aerosol is formed from highly oxygenated low-volatile vapors formed in the gas phase. This is further in line with our studies on the formation and properties of organic aerosol in both chambers and ambient.We have also worked closely with modellers to implement our experimental knowledge on emission oxidation into both atmospheric and chamber models. This work has shown that the low-volatile compounds we discovered in 2014, and which we have continued to characterize, do play a pivotal role in the formation of organic aerosol.
Final results
Through
a. the simultaneous deployment of several different types of chemical ionization mass spectrometers, and
b. advanced statistical analysis techniques, together with
c. close collaboration with leading quantum chemists,
we have collected several valuable data sets which are nearing publication. These concern
1. the role of temperature on the level of oxygenation achieved during oxidation,
2. direct measurements of the condensability of oxidation products,
3. the role of aerosol particle acidity on reactive uptake of more volatile species,
4. the importance of oxidant concentrations on the potential to form organic aerosol from anthropogenic (aromatic) emissions, and
5. the role of nitrogen oxides on the formation and evolution of organic aerosol.
Website & more info
More info: https://www.helsinki.fi/en/researchgroups/atmospheric-physical-chemistry.