Properties and Atmospheric Oxidation of Norpinic Acid Aerosol.

Norpinic acid is a major semi-volatile oxidation product of α-pinene and β-pinene, two of the most important biogenic atmospheric volatile organic compounds. In this study we characterized the physicochemical properties of norpinic acid aerosol using a variety of techniques, and we investigated its reaction with OH radicals. The Aerosol Mass Spectrometer (AMS) spectrum of norpinic acid was characterized by a pronounced peak at m/z 82 (C₅H₆O⁺), which can be used as its chemical signature. The measured density of norpinic acid particles was 1.3 g cm⁻³. Its saturation concentration at 298 K was estimated to be equal to 8.9 μg m⁻³ using thermodenuder measurements and 12.8 μg m⁻³ using isothermal dilution. Its vaporization enthalpy was equal to 71 kJ mol⁻¹. After reaction with OH radicals for an equivalent atmospheric period of 0.6–5 days under UV radiation and low RH, there were no noticeable changes in the AMS spectrum of the particles, while the wall-loss corrected mass concentration slightly decreased. This suggests that the atmospheric aging products of norpinic acid particles are quite similar to the parent molecule when measured by the AMS, and the aging reactions lead to a small change in particle mass concentration. [ABSTRACT FROM AUTHOR]