Temperature and volatile organic compound concentrations as controlling factors for chemical composition of α-pinene-derived secondary organic aerosol

Abstract

Abstract. This work investigates the individual and combined effects of temperature\nand volatile organic compound precursor concentrations on the chemical\ncomposition of particles formed in the dark ozonolysis of α-pinene.\nAll experiments were conducted in a 5\u2009m3 Teflon chamber at an initial\nozone concentration of 100\u2009ppb and initial α-pinene concentrations\nof 10 and 50\u2009ppb, respectively; at constant temperatures of 20, 0, or −15\u2009∘C; and at changing\ntemperatures (ramps) from −15 to 20 and from 20\nto −15\u2009∘C. The chemical composition of the\nparticles was probed using a high-resolution time-of-flight aerosol mass\nspectrometer (HR-ToF-AMS). A four-factor solution of a positive matrix factorization (PMF) analysis of\nthe combined HR-ToF-AMS data is presented. The PMF analysis and the\nelemental composition analysis of individual experiments show that secondary\norganic aerosol particles with the highest oxidation level are formed from\nthe lowest initial α-pinene concentration (10\u2009ppb) and at the\nhighest temperature (20\u2009∘C). A higher initial α-pinene\nconcentration (50\u2009ppb) and/or lower temperature (0 or −15\u2009∘C) results in a lower oxidation level of the molecules contained in\nthe particles. With respect to the carbon oxidation state, particles formed at 0\u2009∘C are more comparable to particles formed at −15\u2009∘C\nthan to those formed at 20\u2009∘C. A remarkable observation is that\nchanges in temperature during particle formation result in only minor\nchanges in the elemental composition of the particles. Thus, the temperature at\nwhich aerosol particle formation is induced seems to be a critical\nparameter for the particle elemental composition. Comparison of the HR-ToF-AMS-derived estimates of the content of organic\nacids in the particles based on m/z\xa044 in the mass spectra show good\nagreement with results from off-line molecular analysis of particle filter\nsamples collected from the same experiments. Higher temperatures are\nassociated with a decrease in the absolute mass concentrations of organic\nacids (R-COOH) and organic acid functionalities (-COOH), while the organic\nacid functionalities account for an increasing fraction of the measured\nparticle mass.\n