Unsaturated organic compounds are emitted in large quantities from natural and human-influenced sources. Atmospheric removal occurs significantly by reaction with ozone, initiating reaction sequences forming free radicals and organic pollutants in the gaseous and particulate phases. Due to their very large number, it is impossible to study the reaction rate for every compound, and most have to be estimated. Updated and extended estimation methods are reported for use in atmospheric models.

We showed that Icelandic dust has a fundamentally different chemical and mineralogical composition from low latitude dust. In particular, magnetite is as high as 1–2 % of the total dust mass. Our results suggest that Icelandic dust may have an important impact on the radiation balance in the sub-polar and polar regions.

We present direct measurements of NO₃ reactivity resulting from the oxidation of isoprene by NO₃ during an intensive simulation chamber study. Measurements were in excellent agreement with values calculated from measured isoprene amounts and the rate coefficient for the reaction of NO₃ with isoprene. Comparison of the measurement with NO₃ reactivities from unstationary-state and model calculations suggests that isoprene-derived RO₂ and HO₂ radicals account for ~ 50 % of overall NO₃ losses.

An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for in situ monitoring of NO₃ radicals in the CSA simulation chamber (at LISA). The optical cavity allows a high sensitivity for NO₃ detection up to 6 ppt for an integration time of 10 seconds. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (with rate constants up to 10-10 cm3 molecule-1 s-1).

The photooxidation of pinonaldehyde is investigated in a chamber study under natural sunlight and low NO conditions with and without an added hydroxyl radical (OH) scavenger. The experimentally determined pinonaldehyde photolysis frequency is faster by a factor of 3.5 than currently used parameterizations in atmospheric models. Yields of degradation products are measured in the presence and absence of OH. Measurements are compared to current atmospheric models and a theory-based mechanism.

When exposed to glyoxal in chamber experiments, dry ammonium or methylammonium sulfate particles turn brown immediately and reversibly without increasing in size. Much less browning was observed on wet aerosol particles, and no browning was observed with sodium sulfate aerosol. While estimated dry aerosol light absorption caused by background glyoxal (70 ppt) is insignificant compared to that of secondary brown carbon overall, in polluted regions this process could be a source of brown carbon.

This study investigates SOA formation and particle growth from α-pinene, limonene and m-cresol oxidation through NO₃ and OH radicals and the effect of relative humidity. The formed SOA is comprehensively characterized with respect to the content of OC/EC, WSOC, SOA-bound peroxides and SOA marker compounds. The findings present new insights and implications of night-time chemistry which can form SOA more efficiently than OH radical reaction during day-time.

In the present study, simulations with the multiphase chemistry model SPACCIM-SpactMod are performed. The investigations aim at assessing the impact of a detailed treatment of non-ideality in multiphase models dealing with aqueous aerosol chemistry. The model studies demonstrate that the inclusion of non-ideality considerably affects the multiphase chemical processing of transition metal ions, oxidants, and related chemical subsystems such as organic chemistry in aqueous aerosols.