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Atmospheric aerosol particles have a profound impact on Earth's climate by scattering and absorbing solar and terrestrial radiation and by impacting the properties of clouds. Research aircraft such as the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) Falcon are widely used to study aerosol particles in the troposphere and lower stratosphere. However, transporting a representative sample to the instrumentation inside the aircraft remains a challenge due to high airspeeds and changing ambient conditions. In particular, for high-quality coarse-mode aerosol measurements, knowledge about losses or enhancements in the aerosol sampling system is crucial. In this study, the sampling efficiency of the aerosol inlet aboard the Falcon research aircraft is characterized for the first time with state-of-the art in situ measurements including sizing instruments operated behind the Falcon aerosol inlet and mounted at the aircraft wing not affected by the aerosol inlet. Sampling efficiencies were derived for different true airspeed ranges by comparing the in-cabin and "full"-size-range particle number size distributions during 174 flight sequences with a major contribution of mineral dust particles during the "Absorbing aerosol layers in a changing climate: aging, lifetime and dynamics" project (A-LIFE). Additionally, experimentally derived Stokes numbers were used to calculate the cutoff diameter of the aerosol sampling system for different particle densities as a function of true airspeed. As expected, the results show that the velocity of the research aircraft has a major impact on the sampling of coarse-mode aerosol particles with in-cabin instruments. For true airspeeds up to about 190 ms-1 , aerosol particles larger than about 1 µm are depleted in the sampling system of the Falcon during the A-LIFE project. In contrast, for true airspeeds higher than 190 ms-1 , an enhancement of particles up to a diameter of 4 µm is observed. For even larger particles, the enhancement effect at the inlet is still present, but inertial and gravitational particle losses in the transport system get more and more pronounced, which leads to a decreasing overall sampling efficiency. In summary, aerosol particles are either depleted or enhanced in the Falcon aerosol inlet, whereas transport in sampling lines always leads to a loss of particles. Here, we have considered both effects and determined the cutoff diameter for the A-LIFE transport system (i.e., the sampling lines only), the cutoff diameter of the Falcon aerosol inlet (i.e., the effect of the inlet only), and the combined effect of the inlet and sampling lines. [ABSTRACT FROM AUTHOR]

Uncertainties in the mineral dust's direct radiative effect arise from the variability in its optical properties. The optical properties can also be influenced by mixing processes with anthropogenic aerosols, such as black carbon or fine particles (called 'pollution' in this study). We aimed to investigate the effect of mixing pollution with mineral dust aerosols from different source regions on the intensive aerosol optical properties. Thus, the Ångström exponents of scattering and absorption (i.e., their wavelength dependence), the single scattering albedo, and the asymmetry parameter were determined from direct optical measurements performed during the A-LIFE aircraft field experiment over the Eastern Mediterranean. This location provided access to Arabian and Saharan dust layers mixed with pollution. Our findings indicated significant changes in all the intensive aerosol optical properties with increasing pollution content within mineral dust layers. Interestingly, the differences between Arabian and Saharan dust's intensive aerosol optical properties were negligible. We discussed the implications of these results for identifying mineral dust events and for their direct radiative effect. First, the mixing with pollution masked the mineral dust signal, suggesting that caution is needed when using the Ångström exponents for identifying mineral dust events. However, the Ångström exponents can help estimate the amount of pollution once a mineral dust event is confirmed. Second, our measurements of the asymmetry parameter and single scattering albedo changed from pure to polluted mineral dust layers (e.g., at 525 nm, the median values decreased from 0.67 to 0.56 and from 0.96 to 0.89, respectively). These changes have 15 opposing effects on the short-wave direct radiative effect efficiency (i.e., the direct radiative effect per unit of aerosol optical depth) and may partly cancel out each other. Nevertheless, the impact of mixing with pollution on the mineral dust's direct radiative effect efficiency can differ depending on the surface albedo. In conclusion, accurate quantification of the pollution content within mineral dust layers is crucial. The pollution significantly impacts mineral dust event identification, its optical properties, and the local direct radiative effect. [ABSTRACT FROM AUTHOR]

Heterogeneous chemical cycles of pyrogenic nitrogen and halides influence tropospheric ozone and affect the stratosphere during extreme Pyrocumulonimbus (PyroCB) events. We report field‐derived N2O5 uptake coefficients, γ(N2O5), and ClNO2 yields, φ(ClNO2), from two aircraft campaigns observing fresh smoke in the lower and mid troposphere and processed/aged smoke in the upper troposphere and lower stratosphere (UTLS). Derived φ(ClNO2) varied across the full 0–1 range but was typically <0.5 and smallest in a PyroCB (<0.05). Derived γ(N2O5) was low in agricultural smoke (0.2–3.6 × 10−3), extremely low in mid‐tropospheric wildfire smoke (0.1 × 10−3), but larger in PyroCB processed smoke (0.7–5.0 × 10−3). Aged biomass burning aerosol in the UTLS had a higher γ(N2O5) of 17 × 10−3 that increased with sulfate and liquid water, but that was 1–2 orders of magnitude lower than values for aqueous sulfuric aerosol used in stratospheric models. Plain Language Summary: The injection of reactive material into Earth's atmosphere from fires affects atmospheric composition at regional and hemispheric scales. Reported stratospheric ozone depletion during extreme events, such as the 2020 Australian wildfires, illustrates one example of fire impacts and the role of heterogeneous (gas‐particle) processes. We report field quantification of rates and product yields from airborne observations of smoke. Extremely slow heterogeneous reaction rates on young smoke increase with transport and aging, but upper atmospheric values are still a factor of 10 slower than parameterizations used in stratospheric models. Heterogeneous production of ClNO2, a major lower atmospheric chlorine activation pathway, may be active on biomass burning aerosol in the upper atmosphere. Key Points: ClNO2 formation is active on biomass burning (BB) particles but decreases with transport to the upper troposphere and lower stratosphere (UTLS)N2O5 uptake coefficients are low on young BB smoke and increase with transport through a PyroCB and UTLS agingN2O5 uptake coefficients on aged BB particles in the UTLS are significantly lower than those used in model parameterizations [ABSTRACT FROM AUTHOR]

Aerosols are key players in the Earth's climate system with mineral dust being one major component of the atmospheric aerosol load. While former campaigns focused on investigating the properties and effects of rather pure mineral dust layers, the A-LIFE (A bsorbing aerosol layers in a changing climate: aging, life time and dynamics) campaign in April 2017 aimed to characterize dust in complex aerosol mixtures. In this study we present ground-based lidar measurements that were performed at Limassol, Cyprus, in April 2017. During our measurement period, the measurement site was affected by complex mixtures of dust from different sources and pollution aerosols from local sources as well as long-range transported. We found mean values of the particle linear depolarization ratio and extinction-to-backscatter ratio (lidar ratio) of 0.27 ± 0.02 and 41 sr ± 5 sr at 355 nm and of 0.30 ± 0.02 and 39 sr ± 5 sr at 532 nm for Arabian dust, and of 0.27 ± 0.02 and 55 sr ± 8 sr at 355 nm and of 0.28 ± 0.02 and 53 sr ± 7 sr at 532 nm for Saharan dust. The values found for pollution aerosols of the particle linear depolarization ratio and the lidar ratio are 0.05 ± 0.02 at 355 nm and 0.04 ± 0.02 at 532 nm, and 65 sr ± 12 sr at 355 nm and 60 sr ± 16 sr at 532 nm, respectively. We use our measurements for aerosol typing and compare that to aerosol typing from sun photometer data, in-situ measurements and trajectory analysis. The different methods agree well for the derived aerosol type, but looking at the derived dust mass concentration from different methods, the trajectory analysis frequently underestimate high dust concentration that were found in major mineral dust events. [ABSTRACT FROM AUTHOR]