Measurements of atmospheric aerosol particles
It is essential to measure physical properties of atmospheric particles in order to describe and quantify their impact on climate, atmospheric chemistry, human health and biogeochemical cycles. The instruments used by RMI are described in the section on Instruments and observation techniques of our group.
Due to the high variability of particle sources and sizes, multiple parameters are necessary to characterise atmospheric particles comprehensively. Measurements of total particle number concentrations and particle sizes are fundamental. Particle size is measured in specific size bins, covering one or more of the above-mentioned size modes, and is typically connected to a sensor for particle number measurement. It results in particle number size distributions, which are the basis for calculating particle surface, volume, and mass size distributions. Particle mass concentrations are important for studies in which mass-related particle properties are relevant (e.g., health-related parameters). Particle mass concentrations are typically given for specific size ranges, e.g., PM10 as the particle mass concentration of particles smaller than 10 µm or PM2.5 as the particle mass concentration of particles smaller than 2.5 µm.
To further characterize the environmental impact of atmospheric particles, their optical properties must be measured. Radiation will be attenuated by atmospheric particles. This attenuation (termed extinction) consists of two parts: particle scattering and absorption. Based on particle scattering and absorption coefficients, additional optical parameters can be derived, e.g. the complex refractive index, the single scattering albedo or the particle phase function, which are essential for studies of the radiative forcing of atmospheric particles or for radiative transfer modeling.
Further, there are specific aerosol instrumentation and measurement principles for characterizing the chemical composition of atmospheric particles.