Coastal aerosols in Scandinavian urban areas remain understudied. We examined aerosol optical properties and size distributions along Denmark's coastline. Combining in situ data with dispersion modelling, we identified two main aerosol types: carbonaceous aerosols from fossil fuel and biomass burning and large, highly scattering aerosols (potentially sea salt). Black carbon from in situ data and dispersion modelling correlated well, while FLEXPART underestimated the concentration.

Seven years of hourly particle number size distributions of 10–500 nanometres were measured at an urban background in Germany. A downward trend of total particle number concentrations of −2 % per year was observed. Wind from the Frankfurt Airport showed the highest nucleation mode particle concentrations. Lockdown lowered the concentration of ultrafine particles in the direction of the airport. On 30 % of all days, the World Health Organization's ultrafine particles value for high concentrations was exceeded.

Small airborne particles influence how clouds form and how they affect the climate. Our study compared eight different instruments that measure the size distributions of these particles to understand the instruments' strengths and weaknesses. We found that some systems are more accurate, whereas others are more sensitive at tiny sizes. These results will help to improve future monitoring of air quality and climate processes.

The measurement of particle mass concentrations in gases is essential for monitoring emissions from engine exhaust or atmospheric pollutants. Various instruments allow for real-time concentration monitoring, but few studies have evaluated the accuracy and reliability of these measurements. We present the results of an intercomparison between several mass concentration measurement instruments to assess their ranges of validity, providing valuable guidance for future users of these devices.

The SiMPLE-PAS is a single-pass, multi-wavelength, portable, and low-expense photoacoustic spectrometer designed to measure absorption of light by atmospheric aerosols. It is differentiated from other PAS instruments by being much less expensive (approximately USD 500 total) and 3D-printed while still allowing measurements at multiple wavelengths. The instrument has competitive detection limits and provides a blueprint for an ultra low-cost PAS to make the technique more accessible.

The first online instrument for the speciation of water‑soluble iron in ambient aerosols is presented. The system combines flow injection analysis with spectrophotometric detection using a liquid waveguide capillary cell. Sensitive iron speciation will help to better describe tropospheric aqueous-phase reactions driven by soluble iron, e.g. hydroxyl radical formation through Fenton chemistry. In first measurements in Berlin, ambient water-soluble-iron concentrations reached up to 47 ng m^-3.

Charged molecular clusters, called small ions, are always present in the atmosphere. Few studies have focused on their size distribution, and, motivated by this, we study the size of small ions and how it varies in Hyytiälä, Finland, and Beijing, China. We find that the relationship between small ion size and low-volatility vapor concentrations is strong in Hyytiälä. In both locations, we find that the small ion size has a positive relationship with cluster formation and growth.

Biomass combustion for domestic heating can contribute to air pollution in residential areas with regard to ultrafine-particle concentrations. Measurements of ultrafine-particle concentrations were performed in a residential area with a diffusion-charge-based device during winter. In the morning and evening hours the concentration increases to, on average, twice the background level. The good-practice statement of a maximum 1 h mean of the World Health Organization is exceeded during 33.6 % of days.

This study examined particle emissions from a large-scale biomass heating plant. Efficient flue gas cleaning, especially with bag-house filters, significantly reduced primary emissions. However, the potential for secondary aerosol formation was found to be 100–1000 times higher than primary emissions, highlighting the need for further research to support air quality and climate goals.

We investigated how water vapor affects the earliest steps of atmospheric aerosol formation, a key process influencing clouds and climate. By benchmarking quantum-chemical methods, we identified reliable approaches for modeling hydrated molecular clusters of common atmospheric acids and bases. We show that humidity moderately stabilizes certain clusters but only modestly alters particle formation rates. These findings sharpen our understanding of clusters and their role in aerosol formation.