Journal: Aerosol Research

Abbreviation

Aerosol Res.

Publisher

Copernicus

Journal Volumes

ISSN

2940-3391

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2024 - 20253
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Publications 1 - 3 of 3
  • Comparison of scanning aerosol lidar and in situ measurements of aerosol physical properties and boundary layer heights
    Item type: Journal Article
    Zhang, Hengheng; Rolf, Christian; Tillmann, Ralf; et al. (2024)
    Aerosol Research
    The spatiotemporal distribution of aerosol particles in the atmosphere has a great impact on radiative transfer, clouds, and air quality. Modern remote sensing methods, as well as airborne in situ measurements by unpiloted aerial vehicles (UAV) or balloons, are suitable tools to improve our understanding of the role of aerosol particles in the atmosphere. To validate the measurement capabilities of three relatively new measurement systems and to bridge the gaps that are often encountered between remote sensing and in situ observation, as well as to investigate aerosol particles in and above the boundary layer, we conducted two measurement campaigns and collected a comprehensive dataset employing a scanning aerosol lidar, a balloon-borne radiosonde with the Compact Optical Backscatter Aerosol Detector (COBALD), an optical particle counter (OPC) on a UAV, and a comprehensive set of ground-based instruments. The extinction coefficients calculated from near-ground-level aerosol size distributions measured in situ are well correlated with those retrieved from lidar measurements, with a slope of 1.037 ± 0.015 and a Pearson correlation coefficient of 0.878, respectively. Vertical profiles measured by an OPC-N3 on a UAV show similar vertical particle distributions and boundary layer heights to lidar measurements. However, the sensor, OPC-N3, shows a larger variability in the aerosol backscatter coefficient measurements, with a Pearson correlation coefficient of only 0.241. In contrast, the COBALD data from a balloon flight are well correlated with lidar-derived backscatter data from the near-ground level up to the stratosphere, with a slope of 1.063 ± 0.016 and a Pearson correlation coefficient of 0.925, respectively. This consistency between lidar and COBALD data reflects the good data quality of both methods and proves that lidar can provide reliable and spatial distributions of aerosol particles with high spatial and temporal resolutions. This study shows that the scanning lidar has the capability to retrieve backscatter coefficients near the ground level (from 25 to 50 m above ground level) when it conducts horizontal measurement, which is not possible for vertically pointing lidar. These near-ground-level retrievals compare well with ground-level in situ measurements. In addition, in situ measurements on the balloon and UAV validated the scanning lidar retrievals within and above the boundary layer. The scanning aerosol lidar allows us to measure aerosol particle distributions and profiles from the ground level to the stratosphere with an accuracy equal to or better than in situ measurements and with a similar spatial resolution.
  • Reactive oxygen species buildup in photochemically aged iron- and copper-doped secondary organic aerosol proxy
    Item type: Journal Article
    Kilchhofer, Kevin; Barth, Alexandre; Utinger, Battist; et al. (2025)
    Aerosol Research
    The toxicity of particulate matter (PM) is highly related to the concentration of particle-bound reactive oxygen species (ROS). Chemical properties, including dissolved metals and the sources of PM, influence ROS production and ROS oxidative potential. Here, the photochemical aging of a secondary organic aerosol proxy (citric acid, CA) with metal complexes (iron–citrate, Fe(III)(Cit)) is assessed toward the production of particle-bound ROS with an online instrument (OPROSI). We studied the photochemically induced redox chemistry in iron/copper–citrate particles experimentally with an aerosol flow tube (AFT), mimicking atmospheric UV aging. Experiments were performed at different relative humidity (RH) levels, leading to variation in the physicochemical properties of the particles, e.g., viscosity. We found that UV-aged CA aerosol containing 10 mol % FeIII generated ROS concentrations on the order of 0.1 nmol H₂O₂ eq. µg⁻¹, indicating the photochemically driven formation of peroxides. An increase in RH leads to only a slight but overall lower concentration of ROS, possibly due to a loss of volatile HO₂ and H₂O₂ in the gas phase in the less viscous particles. The RH effect is enhanced in absence of oxygen. Compared to the FeIII(Cit)/CA particles, the iron/copper–citrate samples show a uniformly decreased ROS level. Interestingly, in the high-RH nitrogen experiment with copper, we found an enhanced drop in the ROS concentration down to 0.02 nmol H₂O₂ eq. µg⁻¹ compared to all other irradiation experiments. We suggest that copper may suppress radical redox reactions, and when particles are more viscous, ROS are still produced with photochemistry, but the levels are more sensitive to the presence of copper than under humid or lower-viscosity conditions.
  • Opinion: Eliminating aircraft soot emissions
    Item type: Journal Article
    Trivanovic, Una; Pratsinis, Sotiris E. (2024)
    Aerosol Research
    Soot from aircraft engines deteriorates air quality around airports and can contribute to climate change primarily by influencing cloud processes and contrail formation. Simultaneously, aircraft engines emit carbon dioxide (CO2), nitrogen oxides (NOx), and other pollutants which also negatively affect human health and the environment. While urgent action is needed to reduce all pollutants, strategies to reduce one pollutant may increase another, calling for a need to decrease, for example, the uncertainty associated with soot's contribution to net radiative forcing (RF) in order to design targeted policies that minimize the formation and release of all pollutants. Aircraft soot is characterized by rather small median mobility diameters, dm=8–60 nm, and at high thrust, low (< 25 %) organic carbon to total carbon (OC/TC) ratios, while at low thrust, the OC/TC can be quite high (> 75 %). Computational models could aid in the design of new aircraft combustors to reduce emissions, but current models struggle to capture the soot, dm, and volume fraction, fv, measured experimentally. This may partly be due to the oversimplification of soot's irregular morphology in models and a still poor understanding of soot inception. Nonetheless, combustor design can significantly reduce soot emissions through extensive oxidation or lean, near-premixed combustion. For example, lean, premixed prevaporized combustors significantly reduce emissions at high thrust by allowing injected fuel to fully vaporize before ignition, while low temperatures from very lean jet fuel combustion limit the formation of NOx. Alternative fuels can be used alongside improved combustor technologies to reduce soot emissions. However, current policies and low supply promote the blending of alternative fuels at low ratios (∼ 1 %) for all flights, rather than using high ratios (> 30 %) in a few flights which could meaningfully reduce soot emissions. Here, existing technologies for reducing such emissions through combustor and fuel design will be reviewed to identify strategies that eliminate them.
Publications 1 - 3 of 3