3 research outputs found
The importance of sesquiterpene oxidation products for secondary organic aerosol formation in a springtime hemiboreal forest
Secondary organic aerosols (SOAs) formed from biogenic volatile organic compounds (BVOCs) constitute a significant fraction of atmospheric particulate matter and have been recognized to significantly affect the climate and air quality. Atmospheric SOA particulate mass yields and chemical composition result from a complex mixture of oxidation products originating from a diversity of BVOCs. Many laboratory and field experiments have studied SOA particle formation and growth in the recent years. However, a large uncertainty still remains regarding the contribution of BVOCs to SOA. In particular, organic compounds formed from sesquiterpenes have not been thoroughly investigated, and their contribution to SOA remains poorly characterized. In this study, a Filter Inlet for Gases and Aerosols (FI-GAERO) combined with a high-resolution time-of-flight chemical ionization mass spectrometer (CIMS), with iodide ionization, was used for the simultaneous measurement of gas-phase and particle-phase oxygenated compounds. The aim of the study was to evaluate the relative contribution of sesquiterpene oxidation products to SOA in a springtime hemiboreal forest environment. Our results revealed that monoterpene and sesquiterpene oxidation products were the main contributors to SOA particles. The chemical composition of SOA particles was compared for times when either monoterpene or sesquiterpene oxidation products were dominant and possible key oxidation products for SOA particle formation were identified for both situations. Surprisingly, sesquiterpene oxidation products were the predominant fraction in the particle phase in some periods, while their gas-phase concentrations remained much lower than those of monoterpene products. This can be explained by favorable and effective partitioning of sesquiterpene products into the particle phase. The SOA particle volatility determined from measured thermograms increased when the concentration of sesquiterpene oxidation products in SOA particles was higher than that of monoterpenes. Overall, this study demonstrates that sesquiterpenes may have an important role in atmospheric SOA formation and oxidation chemistry, in particular during the spring recovery period.Peer reviewe
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Insights into the O : C-dependent mechanisms controlling the evaporation of alpha-pinene secondary organic aerosol particles
Abstract. The volatility of oxidation products of volatile organic
compounds (VOCs) in the atmosphere is a key factor to determine if they
partition into the particle phase contributing to secondary organic aerosol
(SOA) mass. Thus, linking volatility and measured particle composition will
provide insights into SOA formation and its fate in the atmosphere. We
produced α-pinene SOA with three different oxidation levels
(characterized by average oxygen-to-carbon ratio; O:C‾=0.53, 0.69, and 0.96) in an oxidation flow reactor. We investigated the
particle volatility by isothermal evaporation in clean air as a function of
relative humidity (RH <2 %, 40 %, and 80 %) and used a
filter-based thermal desorption method to gain volatility and chemical
composition information. We observed reduced particle evaporation for particles with increasing
O:C‾ ratio, indicating that particles become more resilient to evaporation with
oxidative aging. Particle evaporation was increased in the presence of water
vapour and presumably particulate water; at the same time the resistance of
the residual particles to thermal desorption was increased as well. For SOA
with O:C‾=0.96, the unexpectedly large increase in mean thermal desorption
temperature and changes in the thermogram shapes under wet conditions
(80 % RH) were an indication of aqueous phase chemistry. For the lower
O:C‾ cases, some water-induced composition changes were observed. However, the
enhanced evaporation under wet conditions could be explained by the
reduction in particle viscosity from the semi-solid to liquid-like range, and
the observed higher desorption temperature of the residual particles is a
direct consequence of the increased removal of high-volatility and the
continued presence of low-volatility compounds