AI Article Synopsis
- The study investigates how secondary organic aerosols (SOA) from biogenic volatile organic compounds (VOCs) affect the Earth's climate, focusing on their formation and aging under solar conditions.
- Changes in the chemical composition and thermal properties of SOA were analyzed using mass spectrometry during the aging process, revealing that hydroxyl (OH) exposure was the most significant factor in driving long-term transformations.
- Results indicated that increased OH exposure leads to greater homogeneity in vapor pressure distribution and reduced volatility of the aerosols, as highly volatile components undergo more oxidation compared to less volatile ones.
Article Abstract
Formation and evolution of secondary organic aerosols (SOA) from biogenic VOCs influences the Earth's radiative balance. We have examined the photo-oxidation and aging of boreal terpene mixtures in the SAPHIR simulation chamber. Changes in thermal properties and chemical composition, deduced from mass spectrometric measurements, were providing information on the aging of biogenic SOA produced under ambient solar conditions. Effects of precursor mixture, concentration, and photochemical oxidation levels (OH exposure) were evaluated. OH exposure was found to be the major driver in the long term photochemical transformations, i.e., reaction times of several hours up to days, of SOA and its thermal properties, whereas the initial concentrations and terpenoid mixtures had only minor influence. The volatility distributions were parametrized using a sigmoidal function to determine TVFR0.5 (the temperature yielding a 50% particle volume fraction remaining) and the steepness of the volatility distribution. TVFR0.5 increased by 0.3±0.1% (ca. 1 K), while the steepness increased by 0.9±0.3% per hour of 1×10(6) cm(-3) OH exposure. Thus, aging reduces volatility and increases homogeneity of the vapor pressure distribution, presumably because highly volatile fractions become increasingly susceptible to gas phase oxidation, while less volatile fractions are less reactive with gas phase OH.
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| http://dx.doi.org/10.1021/es405412p | DOI Listing |
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