Secondary organic aerosol from oxidation of camphene with ozone and OH radicals – kinetics, yields and molecular composition at 313 – 243K

Non-methane volatile organic compounds (NMVOCs) emissions are dominated by biogenic VOC (BVOC) primarily from vegetation emissions. Main compounds are isoprene and monoterpenes which are precursors to tropospheric ozone and secondary organic aerosols, leading to impacts on air quality, human health, visibility and climate change both directly and indirectly.

Camphene is an abundant monoterpene which has been understudied, particularly in terms of its kinetics, secondary organic aerosol (SOA) yields and molecular composition (Gaona-Colmán et al., 2017; Afreh et al., 2021; Li et al., 2022). Here, we present a systematic study of SOA formation from Camphene over a wider temperature range (243 K – 313K) by dedicated simulation chamber experiments. We used ozone concentrations of 2.18–3.72 ppm for camphene oxidation, representing a substantial excess of ozone, to a allow a significant chemical conversion at relative low reaction rates.

Based on PTR-MS (PTR-MS 4000, Ionicon Analytik GmbH) measurements of camphene and acetone concentrations as well as ozone measurements (Environment 0341M), the rate coefficients of the reaction of camphene with ozone and OH radicals were determined by fitting the results of a kinetic model to the observations. Particle size distributions and number concentrations were measured by a scanning mobility particle sizer (SMPS) utilizing a differential mobility analyser (DMA; 3071, TSI Inc.) coupled to a CPC (3772, TSI Inc.). Particle number concentrations were measured by two condensation particle counters (3022A and 3776, TSI Inc.). The particle number size distributions of the SMPS were corrected for the total number concentration measured by a calibrated CPC and used to calculate the SOA mass concentration by applying an effective particle density of 1.3 (Li et al., 2022). SOA mass concentrations were also measured with a HR-ToF-AMS (Aerodyne Inc.) SOA yields (YSOA) were calculated as YSOA = ΔMorg/ΔVOC, where ΔMorg is the SOA mass formed from the reacted mass of camphene (ΔVOC).

A chemical ionization mass spectrometer coupled with a filter inlet for gases and aerosols (FIGAERO-CIMS,  Aerodyne Inc) was used to measure both gas-phase and particle phase chemical composition employing iodide as reagent ion. Particles were collected on prebaked Teflon filters (1 µm, SKC Inc.) using a stainless-steel filter holder for offline analysis.

Major secondary organic aerosol products and different chemical components of the gas and particle phase present at all temperatures were resolved. The variation in the abundance of individual organic molecules during ozonolysis and OH radical initiated oxidation were resolved at four different temperatures: 243, 273, 298, 313 K. This presentation will discuss the main findings in the context of previous studies as well as its implications for the role of camphene in atmospheric aerosol chemistry.

 

Afreh et al., Atmos. Chem. Phys., 21, 11467–11487, 2021.

Gaona-Colmán et al., RSC Adv., 7, 2733-2744, 2017.

Li et al., Atmos. Chem. Phys., 22(5), 3131–3147, 2022