Abstract
Abstract. Large-scale atmospheric models, which typically describe secondary organic aerosol (SOA) formation based on chamber experiments, tend to systematically underestimate observed organic aerosol burdens. Since SOA constitutes a significant fraction of atmospheric aerosol, this discrepancy translates into an underestimation of SOA contribution to radiative forcing of atmospheric aerosol. Here we show that the underestimation of SOA yields can be partly explained by wall losses of SOA forming compounds during chamber experiments. We present a chamber experiment where α-pinene and ozone are injected into a Teflon chamber. When these two compounds react, we observe rapid formation and growth of new particles. Theoretical analysis of this formation and growth event indicates rapid formation of oxidized volatile organic compounds (OVOC) of very low volatility in the chamber. If these oxidized organic compounds form in the gas phase, their wall losses will have significant implications on their partitioning between the gas and particle phase. Although these OVOCs of very low volatility contribute to the growth of new particles, their mass will almost completely be depleted to the chamber walls during the experiment, while the depletion of OVOCs of higher volatilities is less efficient. According to our model simulations, the volatilities of OVOC contributing to the new particle formation event can be of the order of 10−5 μg m−3.
Highlights
Organic chemical compounds modify the physical and chemical properties of atmospheric aerosol particles, namely, their radiative properties, their ability to act as cloud condensation nuclei, and heterogeneous chemistry
Organic aerosol can be emitted directly into the atmosphere as primary particles, e.g. from fossil fuel and biomass combustion, or it can be of secondary origin; when volatile organic compounds (VOC) are oxidized in the atmosphere, they produce oxidized volatile organic compounds (OVOC) which condense onto pre-existing aerosolforming secondary organic aerosol (SOA)
The gas-wall equilibrium as a function of saturation vapor pressure of the OVOCs was determined by measuring the fraction of the injected compounds remaining in the gas phase
Summary
Organic chemical compounds modify the physical and chemical properties of atmospheric aerosol particles, namely, their radiative properties, their ability to act as cloud condensation nuclei, and heterogeneous chemistry. Organic compounds (OC) amount to a significant fraction of atmospheric aerosol mass. In several observations at different types of locations, the measured mass fraction of organic compounds can be 20–90 % in collected aerosol samples (Jimenez et al, 2009). OC has a major role in the climate effects of global atmospheric aerosol. SOA compounds affect the size distribution, radiative properties, and cloud activation properties of atmospheric particles. Their contribution to the global aerosol mass and composition play a key role in the climate effects of the atmospheric aerosol. A bottom-up approach tends to underestimate the global burden of SOA when compared to the observations or compared to studies where global SOA burdens are determined inversely based on VOC
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