Investigating the chemical composition of wildfire smoke particles using advanced single-particle mass spectrometry

Open fires have strong impacts on air quality, human health, climate and the earth. These aerosols are complex and highly variable in their atmospheric aging and distribution. Chemical transformations play a crucial role in influencing climate and health outcomes by affecting the optical and radiative properties of particles, cloud condensation activity, and biological effects. We have developed laser ionization schemes that exploit resonances between the incident laser light and particle-bound molecules and atoms in single-particle mass spectrometry (SPMS). These new methods allow intriguing investigations of smoke particles from wildfires. In a wildfire model, we studied the emissions from typical vegetation from the boreal forest and African savannah. For the water-soluble phase that contributes to the cloud-condensation activity, we could show that glyoxal and methylglyoxal are emitted directly from the combustion process and we observed the time-resolved formation of oxalate during chamber ageing. For the climate- and health-relevant polycyclic aromatic hydrocarbons (PAH) we found high concentrations of the softwood combustion marker retene in boreal forest emissions as well as its rapid degradation during ageing. In addition to the organic particle content, we present the inorganic composition of the particles on a single-particle basis, which revealed high concentrations of potassium and sulphate in the savannah fuels. These components appear to have a significant effect on the hygroscopicity of the particles and thus on their cloud condensation nucleation (CCN) potential. Beyond lab experiments, we show how our SPMS method can detect biomass burning particles in the atmosphere in real time and demonstrate its potential for risk assessment, source apportionment and research on atmospheric transport and processing.