Characterization of an indoor environmental chamber and identification of C₁–C₄ OVOCs during isoprene ozonolysis

Abstract

An environmental chamber was built up and characterized at The Hong Kong Polytechnic University. The chamber consists of a 6 m3 poly tetrafluoroethylene-co-perfluoropropyl vinyl ether Teflon film reactor inside a stainless-steel enclosure stocked with a series of online gas-phase and aerosol-phase analytical instruments. Temperature and relative humidity are controllable and can be set to a range of 10–40 ± 1°C and 5–85%, ± 3%, respectively. An air purification system provides zero air for the chamber with concentrations of total volatile organic compounds < 1 ppb, NOX and O₃ < 1 ppb and particles concentration < 102 particles·cm−3. Characterization experiments were performed under dry conditions (relative humidity< 5%) and ambient temperature (25°C). Average wall loss rates of O₃ and NO₂ were observed as 2.92 × 10⁻⁶ s⁻¹ and 9.3 × 10⁻⁴ s¹ respectively, and the particle wall loss rate was 0.27 h−1. Dark ozonolysis of isoprene was studied using this chamber and the production of C₁–C₄ oxygenated volatile organic compounds such as formaldehyde, methacrolein and methyl vinyl ketone (MVK) was identified using proton-transfer-reaction time-of-flight mass spectrometry. Results of experiments indicate that this new facility can be used to investigate and simulate the gaseous chemistry and secondary aerosol formation.