Accurately Quantifying Gas/Particle Partitioning in Environmental Chambers Despite Wall Losses
New technique separates effects of chamber from reacting aerosol to improve measurement of chemical yields of atmospherically relevant products.
For decades, environmental “smog” chambers have been used to determine how much secondary organic aerosol (SOA) can form from certain gaseous emissions and to study their chemistry. But in recent years, it has become clear that gases can stick to the walls of the bag, which can change the results of particle chamber experiments. The researchers provide an experimental method for studying aerosol formation from gases while taking into account their losses to the walls.
This experimental method for studying gas/particle partitioning in environmental chambers allows researchers to track the fates of molecules as gases and particles through a chamber experiment. This allows study of fundamental behaviors of gas- and particle-phase compounds and assessment of potential underestimation of secondary aerosol production due to wall losses in the chamber. These techniques may help researchers design better future chamber experiments and increase precision of aerosol yield measurements.
Gas/particle partitioning is a critical atmospheric process that remains extremely difficult to measure in the atmosphere, and even in atmospheric environmental chambers. In this work, researchers oxidize known precursors to produce fast bursts of multiple low-volatility compounds. By injecting different amounts of liquid organic seed aerosol into the chamber and tracking the rate of decrease of the gases in high time resolution, they model the gas/particle partitioning including both gas- and particle-phase wall losses. Different amounts of aerosol “condensational sinks” show different rates of gas-phase decrease, indicating that the effect of gas/particle partitioning is clearly separable from gas/wall partitioning and therefore measurable in chamber experiments. The experiments extract a measurement of the mass accommodation coefficient (a key parameter in aerosol models that represents the probability that a gas molecule will stick in the aerosol) for multiple different compounds. Because older measurements of the accommodation coefficient are very difficult and vary by many orders of magnitude, the current experiments offer additional precision beyond what was previously available, suggest the accommodation coefficient is close to 1 for the organic aerosols studied, and allow estimation of potential underestimation of products for these reactions.
University of Colorado, Boulder
Funding for this work was provided by DOE (BER/ASR) DESC0011105 and DE-SC0016559, DOE (SBIR) DESC0011218, NSF AGS-1360834, NSF AGS-1420007, and an EPA STAR graduate fellowship (FP-91770901-0).
Krechmer, J., D. Day, P. Ziemann, and J. Jimenez. “Direct Measurements of Gas/Particle Partitioning and Mass Accommodation Coefficients in Environmental Chambers.” Environmental Science & Technology, 51(20), (2017). doi:10.1021/acs.est.7b02144