Quantifying the influence of IVOC and SVOC on ambient SOA formation

Intermediate and semivolatile organic compounds (IVOC and SVOC) play a pivotal role in atmospheric secondary organic aerosol (SOA) formation, contributing substantially to fine particulate matter that impacts air quality, climate, and human health. Anthropogenic IVOC, such as hydrocarbons from diesel vehicle emissions, undergo rapid oxidation to yield low-volatility products that partition into aerosols. Similarly, also biogenic IVOC and SVOC like sesquiterpenes emitted from plants enhance SOA yields in forested regions. Quantifying their contributions to SOA formation remains challenging due to detection limitations, underscoring the need for advanced analytical methods. 

To elucidate the atmospheric fate of IVOC and SVOC, we herein combine a dynamic volatility separation technique with a novel flow-reactor for rapid photochemical oxidation and two FUSION PTR-TOF instruments (IONICON Analytik, Austria) for characterizing gas-phase and condensed organic compounds.

The gas-phase volatility separation technique was recently introduced by Morris et al. (2024). This method utilizes the well studied absorption processes of low volatiles onto polymer tubing to separate volatility classes. Hence, via dynamic addition and removal of absorbing polymer tubing, a defined fraction of SVOC and IVOC can be efficiently removed from complex mixtures as present in ambient air. We further improved this method by using an actively cooled conductive PTFE inlet as a volatility separator. Hence, the volatility cutoff to organic precursors can be precisely adjusted by temperature without the need to switch between different types of polymer.

To study the SOA formation potential with and without IVOC and SVOC, this optimized volatility separator is periodically added prior to injection of ambient air into the novel IONICON Laminar-flow Oxidation reactor (ILOx) for rapid photochemical ageing. ILOx’s design allows for transmitting particles, IVOC and even SVOC with lowermost losses. All wetted surfaces are passivated, providing best response times, even for reduced volatility gas-phase organics. 

The ambient air pre and post ILOx is analyzed by two FUSION PTR-TOF, one equipped with a CHARON particle inlet, and a SMPS system (Grimm Aerosol Technik, Germany). For gas-phase measurements, the instruments cover the volatility range from VOC to SVOC and offer limits of detection in the range of 100 ppqV. With the CHARON particle inlet also condensed organics are detected on a molecular composition level at highest analytical precision and lowermost limits of detection (~20 pg/m³).

In this presentation we will highlight the capabilities of this new method with an example of a morning rush-hour event in Innsbruck, Austria. Hydrocarbons and aromatic hydrocarbons emitted by vehicles are significantly elevated. Most of these traffic related volatile organics can be classified as volatile and only approximately 13% can be attributed to IVOC and SVOC. Our method allows us to precisely quantify the contribution of this relatively small fraction to the potential SOA formation, revealing an overproportional impact on the SOA yield.

Morris et al.: Absorption of volatile organic compounds (VOCs) by polymer tubing: implications for indoor air and use as a simple gas-phase volatility separation technique, Atmos. Meas. Tech., 17, 1545–1559, https://doi.org/10.5194/amt-17-1545-2024, 2024.