Showing papers by "Eija Asmi published in 2023"

A full year of aerosol size distribution data from the central Arctic under an extreme positive Arctic Oscillation: insights from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition

Abstract: Abstract. The Arctic environment is rapidly changing due to accelerated warming in the region. The warming trend is driving a decline in sea ice extent, which thereby enhances feedback loops in the surface energy budget in the Arctic. Arctic aerosols play an important role in the radiative balance and hence the climate response in the region, yet direct observations of aerosols over the Arctic Ocean are limited. In this study, we investigate the annual cycle in the aerosol particle number size distribution (PNSD), particle number concentration (PNC), and black carbon (BC) mass concentration in the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. This is the first continuous, year-long data set of aerosol PNSD ever collected over the sea ice in the central Arctic Ocean. We use a k-means cluster analysis, FLEXPART simulations, and inverse modeling to evaluate seasonal patterns and the influence of different source regions on the Arctic aerosol population. Furthermore, we compare the aerosol observations to land-based sites across the Arctic, using both long-term measurements and observations during the year of the MOSAiC expedition (2019–2020), to investigate interannual variability and to give context to the aerosol characteristics from within the central Arctic. Our analysis identifies that, overall, the central Arctic exhibits typical seasonal patterns of aerosols, including anthropogenic influence from Arctic haze in winter and secondary aerosol processes in summer. The seasonal pattern corresponds to the global radiation, surface air temperature, and timing of sea ice melting/freezing, which drive changes in transport patterns and secondary aerosol processes. In winter, the Norilsk region in Russia/Siberia was the dominant source of Arctic haze signals in the PNSD and BC observations, which contributed to higher accumulation-mode PNC and BC mass concentrations in the central Arctic than at land-based observatories. We also show that the wintertime Arctic Oscillation (AO) phenomenon, which was reported to achieve a record-breaking positive phase during January–March 2020, explains the unusual timing and magnitude of Arctic haze across the Arctic region compared to longer-term observations. In summer, the aerosol PNCs of the nucleation and Aitken modes are enhanced; however, concentrations were notably lower in the central Arctic over the ice pack than at land-based sites further south. The analysis presented herein provides a current snapshot of Arctic aerosol processes in an environment that is characterized by rapid changes, which will be crucial for improving climate model predictions, understanding linkages between different environmental processes, and investigating the impacts of climate change in future Arctic aerosol studies.

Collective geographical ecoregions and precursor sources driving Arctic new particle formation

Abstract: Abstract. The Arctic is a rapidly changing ecosystem, with complex ice–ocean–atmosphere feedbacks. An important process is new particle formation (NPF), from gas-phase precursors, which provides a climate forcing effect. NPF has been studied comprehensively at different sites in the Arctic, ranging from those in the High Arctic and those at Svalbard to those in the continental Arctic, but no harmonised analysis has been performed on all sites simultaneously, with no calculations of key NPF parameters available for some sites. Here, we analyse the formation and growth of new particles from six long-term ground-based stations in the Arctic (Alert, Villum, Tiksi, Zeppelin Mountain, Gruvebadet, and Utqiaġvik). Our analysis of particle formation and growth rates in addition to back-trajectory analysis shows a summertime maxima in the frequency of NPF and particle formation rate at all sites, although the mean frequency and particle formation rates themselves vary greatly between sites, with the highest at Svalbard and lowest in the High Arctic. The summertime growth rate, condensational sinks, and vapour source rates show a slight bias towards the southernmost sites, with vapour source rates varying by around an order of magnitude between the northernmost and southernmost sites. Air masses back-trajectories during NPF at these northernmost sites are associated with large areas of sea ice and snow, whereas events at Svalbard are associated with more sea ice and ocean regions. Events at the southernmost sites are associated with large areas of land and sea ice. These results emphasise how understanding the geographical variation in surface type across the Arctic is key to understanding secondary aerosol sources and providing a harmonised analysis of NPF across the Arctic.

How horizontal transport and turbulent mixing impacts aerosol particle and precursor concentrations at a background site in the UAE

Abstract: ,

Ice nucleating particle measurement at Helsinki

Abstract: Ice nucleating particles (INPs) are particles in the atmosphere that are able to initiate the freezing of water droplets, a process known as ice nucleation. INPs are important to study because they play a crucial role in many atmospheric processes, including the formation of clouds, precipitation, and the radiative properties of clouds. For example, INPs can influence the concentration, size, and shape of ice crystals in clouds, which can in turn affect the reflectivity and lifetime of the clouds. This can have significant impacts on Earth's radiative balance and climate. The most relevant process of ice crystal formation in mixed-phase clouds (MPC) is by immersion freezing (Ansmann et al., 2009). Immersion freezing takes place when an INP is immersed in a water droplet and freezing is triggered on the particle's surface. In this research, we present a series of INP concentration measurements obtained using a novel assay under development at the Finnish Meteorological Institute in Helsinki. The focus of our research is to evaluate the consistency and replicability of these measurements.  To determine the contribution of different aerosols to the INP spectrum at different temperatures, we collect atmospheric particles onto membrane filters and analyze the concentration of INPs in a laboratory freezing experiment. In this experiment, we produce an aqueous solution with collected atmospheric particles and monitor identical aliquots of the aqueous solution while they are cooled until freezing. Finally, using the frozen fraction of aliquots at a given temperature, the volume of each aliquot, and the sample's air volume, the cumulative number of INPs in the given sample at each temperature is calculated following (Vali, 2019). Three automatic samplers were run in parallel to collect particles onto the membrane filters using different sampling schemes. For example, collecting daily samples with three different sampling flows. With these measurements, we will analyze the influence of the sampled air volume, air flow, and sampling duration on the INP concentration measurements. ReferencesAnsmann, A. et al. (2009) Evolution of the ice phase in tropical altocumulus: SAMUM lidar observations over Cape Verde Atmosphere, 9(9), 357Vali, G., (2019). Revisiting the differential freezing nucleus spectra derived from drop-freezing experiments: Methods of calculation, applications, and confidence limits. Atmos. Meas. Tech., 12(2), 1219-1231. https://doi.org/10.5194/amt-12-1219-2019

The Four-Wavelength Photoacoustic Aerosol Absorption Spectrometer PAAS-4λ

Abstract: Light absorbing particulate emissions, known as black carbon (BC) or brown carbon (BrC), are major contributors to the atmospheric aerosol and have a significant impact on climate forcing. The spectral light absorption coefficient of these particles, which is essential for understanding their impact on the climate, can vary greatly depending on the combustion process and atmospheric aging, particularly in the Arctic where concentrations of BC and BrC are low but the climate is sensitive to changes in the atmospheric aerosol. Traditional filter-based methods for characterizing light absorbing aerosol can be prone to errors in environments where the relationship between particle light scattering and absorption is high due to cross-sensitivity to co-deposited light scattering particles. The photoacoustic absorption spectroscopy (PAS) method is less sensitive to particle light scattering and has a high measurement precision and accuracy, but is not widely used for long-term monitoring due to ist assumed lack of sensitivity and robustness.The Photoacoustic Aerosol Absorption Spectrometer PAAS-4λ has been developed for use in unattended air quality monitoring stations and utilizes four wavelengths coupled to a single acoustic resonator in a compact and robust design. It has a low detection limit of below 0.1 Mm-1 and has been calibrated in the laboratory using NO2/air mixtures and Nigrosin aerosol. The PAAS-4λ has been validated at an air quality monitoring station in the European Arctic and its performance during 12 months of deployment is presented. Comparisons with filter-based photometers demonstrate the capabilities and value of the PAAS-4λ for both long-term monitoring and the validation of filter-based instruments.

Inherently Charged Particle (ICP) Sensor Design

Abstract: Ambient particles from natural and anthropogenic sources are a major cause of premature deaths globally. While there are many instruments suitable for scientific measurements of aerosols, better methods for long-term monitoring purposes are still needed, especially low-maintenance, affordable solutions for ultrafine particles. In this article, we present a new sensor design and prototype, the inherently charged particle (ICP) sensor, which uses the preexisting electrical charge of particles to measure particle concentration, instead of employing a charging mechanism, as is typical for instruments based on electrical detection. When the ICP-sensor is employed in conjunction with another instrument, information on the particle charge state can also be derived. We present the results of a laboratory characterization as well as two measurements in suggested applications: 1) engine exhaust measurements and 2) ambient measurements in a traffic environment, where we compare the sensor response to three particle concentration metrics: 1) number; 2) surface area; and 3) mass. The sensor proved suitable for both applications, the signal correlated best with number concentration in the engine emission measurements and with particle surface area in the ambient measurements. The measured charge concentrations were well-correlated ( ${R}^{\,2} >0.8$ ) with theoretical values calculated from the number size distribution assuming an equilibrium charge distribution.

How horizontal transport and turbulent mixing impacts aerosol particle and precursor concentrations at a background site in the UAE

Abstract: Abstract. Aerosol particle optical, physical and chemical properties have been previously studied in the United Arab Emirates (UAE), but there is still a gap in the knowledge of particle sources, and in the horizontal and vertical transport of aerosol particles and their precursors in the area. To investigate how aerosol particle and SO2 concentrations at the surface responded to changes in horizontal and vertical transport, we used data from a one-year measurement campaign at a background site where local sources of SO2 where expected to be minimal. The measurement campaign provided a combination of in-situ measurements at the surface, and the boundary layer evolution from vertical and horizontal wind profiles measured by a Doppler lidar. The diurnal structure of the boundary layer in the UAE was very similar from day to day, with deep well-mixed boundary layer during the day transitioning to a shallow nocturnal layer, with the maximum boundary layer height usually being reached around 1400 local time. Both SO2 and nucleation mode aerosol particle concentrations were elevated for surface winds coming from the east or western sectors. We attribute this to oil refineries located on the eastern and western coasts of the UAE. The concentrations of larger cloud condensation nuclei (CCN) sized particles and their activation fraction did not show any clear dependence on wind direction, but the CCN number concentration showed some dependence on wind speed, with higher concentrations coinciding with the weakest surface winds. Peaks in SO2 concentrations were also observed despite low surface wind speeds and wind directions unfavourable for transport. However, winds aloft were much stronger, with wind speeds of 10 m s-1 at 1 km common at night, and with wind directions favourable for transport, and surface-measured concentrations increased rapidly once these particular layers started to be entrained into the growing boundary layer, even if the surface wind direction was from a clean sector. These conditions also displayed higher nucleation mode aerosol particle concentrations, i.e. new particle formation events occurring due to the increase in the gaseous precursor.

The Four-Wavelength Photoacoustic Aerosol Absorption Spectrometer PAAS-4λ

Abstract: Abstract. In this paper the Photoacoustic Aerosol Absorption Spectrometer PAAS-4λ is introduced. PAAS-4λ was specifically developed for long-term monitoring tasks in (unattended) air quality stations. It uses four wavelengths coupled to a single acoustic resonator in a compact and robust set-up. The instrument has been thoroughly characterized and carefully calibrated in the laboratory using NO2/air mixtures and Nigrosin aerosol. It has an ultimate 1σ detection limit below 0.1Mm-1 at a measurement precision and accuracy of 3 % and 10 %, respectively. In order to demonstrate the PAAS-4λ suitability for long-term monitoring tasks, the instrument is currently validated at the air quality monitoring station Pallas in Finland, about 140 km north of the Arctic circle. Eleven months of PAAS-4λ data from this deployment are presented and discussed in terms of instrument performance. Intercomparisons with the filter-based photometers COSMOS, MAAP, and AE33 demonstrate the capabilities and value of PAAS-4λ, also for the validation of the widely used filter-based instruments.

The four-wavelength Photoacoustic Aerosol Absorption Spectrometer (PAAS-4λ)

Abstract: Abstract. In this paper, the Photoacoustic Aerosol Absorption Spectrometer (PAAS-4λ) is introduced. PAAS-4λ was specifically developed for long-term monitoring tasks in (unattended) air quality stations. It uses four wavelengths coupled to a single acoustic resonator in a compact and robust set-up. The instrument has been thoroughly characterized and carefully calibrated in the laboratory using NO2/air mixtures and Nigrosin aerosol. It has an ultimate 1σ detection limit below 0.1 Mm−1, at a measurement precision and accuracy of 3 % and 10 %, respectively. In order to demonstrate the PAAS-4λ suitability for long-term monitoring tasks, the instrument is currently validated at the air quality monitoring station Pallas in Finland, about 140 km north of the Arctic circle. A total of 11 months of PAAS-4λ data from this deployment are presented and discussed in terms of instrument performance. Intercomparisons with the filter-based photometers of a continuous soot monitoring system (COSMOS), the Multi-Angle Absorption Photometer (MAAP), and Aethalometer (AE33) demonstrate the capabilities and value of PAAS-4λ, as well as for the validation of the widely used filter-based instruments.