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A schematic diagram of the aerosol generation and measurement setup at atmospheric pressure conditions. The calibration aerosol was generated either in a flow tube reactor or the atomizer. Apart from PSL, all atomized particles were sent through a diffusion drier to DMA for size selection, while PSL particles were delivered from the atomizer directly to both UHSAS instruments following dilution with dry air.
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Atmospheric aerosol is a key component of the chemistry and climate of the Earth's atmosphere. Accurate measurement of the concentration of atmospheric particles as a function of their size is fundamental to investigations of particle microphysics, optical characteristics, and chemical processes. We describe the modification, calibration, and perfo...
Citations
... The ATom AOD and aerosol property data set is elaborated in Brock et al. (2021aBrock et al. ( , 2021b, therefore only brief description is provided here. The aerosol size distribution measurements were described in detail elsewhere (Brock et al., 2019;Kupc et al., 2018;Williamson et al., 2018). The composition-dependent aerosol size distribution, covering nucleation/Aitken/accumulation/coarse modes, is determined by combining the size distribution with single-particle (Particle Analysis by Laser Mass Spectroscopy [PALMS]) and bulk (High Resolution Time-Of-Flight Aerosol Mass Spectrometer: HR-ToF-AMS) compositions, as well as black carbon (Single Particle Soot Photometer: SP2). ...
Aerosol optical depth (AOD) is a vital parameter in atmospheric research. Using observations of the Visible Infrared Imaging Radiometer Suite (VIIRS), onboard Suomi National Polar‐orbiting Partnership (Suomi‐NPP) and NOAA‐20 satellites, National Oceanic and Atmospheric Administration (NOAA) produces near‐real time AOD product with high pixel resolution (750 m), wide swath width (3,040 km), and a 16‐day repeat cycle. Here we report the evaluation of the NOAA/VIIRS AOD using a comprehensive aerosol data set, derived from a global‐scale, multi‐seasonal airborne mission, the NASA Atmospheric Tomography Mission (ATom). This data set includes rich physical and chemical information, such as size distributions, chemical compositions, optical properties, and hygroscopicities of major aerosol types, including dust, sea salt, smoke, internally mixed sulfate/nitrate/organics particles (non‐smoke), black carbon, etc. Globally, VIIRS AOD (Suomi‐NPP and NOAA‐20) shows good agreement with the ATom AOD in the moderate to high AOD range (>0.3), with respect to measurement uncertainties (orthogonal distance regression fitting slope: 1.5 ± 0.2 for Suomi‐NPP and 1.6 ± 0.5 for NOAA‐20; correlation coefficient: 0.85 for Suomi‐NPP and 0.73 for NOAA‐20). There is a persistent bias in the low AOD range (<0.3) on the order of 0.03, likely reflecting systematic errors on VIIRS and/or the ATom AOD product. Ångström exponent reported by VIIRS shows excellent agreement with ATom results within expected uncertainties. Given the unique insights revealed by the ATom AOD and aerosol property data set, it is desirable to have ATom‐like comprehensive payloads in future airborne satellite validation programs.
... Atmospheric aerosol substantially influences human health (Oberdörster et al., 2005;WHO, 2016) and our climate (e.g., IPCC, 2021IPCC, , 2013. Therefore, it is constantly monitored either by ground-based measurement stations (such as Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS) and Global Atmosphere Watch (GAW); Asmi et al., 2013;Rose et al., 2021) or by aircraft measurements (IAGOS, the ATOM mission, A-LIFE, and many other ones; Bundke et al., 2015;Williamson et al., 2018;Brock et al., 2019;Kupc et al., 2018;Weinzierl et al., 2017;Thompson et al., 2022;Schöberl et al., 2023). The particle number concentration is an important parameter for quantifying the abundance of these short-lived atmospheric components. ...
One of the most important parameters to quantify an aerosol is the particle number concentration. Condensation particle counters (CPCs) are commonly used to measure the aerosol number concentration in the nanometer size range. To compare the data from different measurement stations and campaigns, it is important to harmonize the instrument specifications, which is why the CEN/TS 16976:2016 technical specification was introduced for CPCs. Therein, the parameters of the CEN CPC are specified for standard pressure and temperature. However, CEN CPCs are used in various surroundings, on high mountains or on airplanes, where they are exposed to low-pressure conditions. Here, we present the pressure-dependent performance (including the concentration linearity and counting efficiency) of two different models of CEN CPCs, the Grimm 5410 CEN and the TSI 3772 CEN. We found that their performance at 1000 and 750 hPa was in accordance with the CEN technical specifications. Below 500 hPa, the performance decreased for both CPC models, but the decrease was different for the two models. To gain insight into the performance of the two CPC models, we performed a simulation study. This study included simulations of the saturation profiles and calculations of internal particle losses within the CPCs. The simulations reproduced the overall performance decrease with decreasing pressure and reveal that the internal structure of the CPC has a significant influence on the performance. We anticipate our publication to provide a deeper understanding of the counting efficiency of CPCs and their pressure dependence. Our findings might be a starting point for new standards that include the pressure-dependent performance, or they could help in designing new CPCs.
... We note that the same company which produces the SP2 produces a commercial OPS, the ultra-high sensitivity aerosol spectrometer (UHSAS), which is similar to the SP2 OPS. Studies on the UHSAS may provide some insights into particle behaviour in the SP2 OPS (Kupc et al., 2018;Howell et al., 2021;Moore et al., 2021a), although lightscattering signals in the SP2 are typically analyzed in a time-resolved manner to account for evaporation (e.g. Gao et al., 2007;Moteki and Kondo, 2007;Laborde et al., 2012;Taylor et al., 2015). ...
... During SOCRATES, size-resolved number concentrations of accumulation mode particles were measured using a wing-mounted Ultra-High Sensitivity Aerosol Spectrometer (WM-UHSAS, Droplet Measurement Technologies, Kupc et al., 2018;Laboratory, 2019b; Table 1). An additional UHSAS instrument (CVI-UHSAS) was located downstream of the counter flow virtual impactor (CVI) inlet (C. ...
Southern Ocean (SO) low‐level mixed phase clouds have been a long‐standing challenge for Earth system models to accurately represent. While improvements to the Community Earth System Model version 2 (CESM2) resulted in increased supercooled liquid in SO clouds and improved model radiative biases, simulated SO clouds in CESM2 now contain too little ice. Previous observational studies have indicated that marine particles are major contributor to SO low‐level cloud heterogeneous ice nucleation, a process that initiates a number of cloud processes that govern cloud radiative properties. In this study, we utilize detailed aerosol and ice nucleating particle (INP) measurements from two recent measurement campaigns to assess simulated aerosol abundance, number size distributions, and composition and INP parameterizations for use in CESM2. Our results indicate that CESM2 has a positive bias in simulated surface‐level total aerosol surface area at latitudes north of 58°S. Measured INP populations were dominated by marine INPs and we present evidence of refractory INPs present over the SO assumed here to be mineral dust INPs. Results highlight a critical need to assess simulated mineral dust number and size distributions in CESM2 in order to adequately represent SO INP populations and their response to long‐term changes in atmospheric transport patterns and land use change. We also discuss important cautions and limitations in applying a commonly used mineral dust INP parameterization to remote regions like the pristine SO.
... It must be noted that rapid change of pressure might affect the sample flow measurement and, consequently, the quantification of aerosol particle number concentration by the UHSAS (Brock et al., 2011). Although modification of the UHSAS flow system are recommended for airborne operation (Kupc et al., 2018), Schulz et al. (2019) 185 showed no measuring bias of unmodified UHSAS during low-speed flights installed in the unpressurized cabin of Polar 6. ...
Aerosol-cloud interaction is considered one of the largest sources of uncertainties in radiative forcing estimations. To better understand the role of black carbon aerosol as cloud nucleus and the impact of clouds on its vertical distribution in the Arctic, we report airborne in-situ measurements of refractory black carbon aerosol particles (rBC) in the European Arctic near Svalbard during the ACLOUD campaign held in summer 2017. rBC was measured with a single particle soot photometer on board of the research aircraft “Polar 6” from the lowest atmospheric layer up to approximately 3500 m asl. During in-cloud flight transects, rBC particles contained in liquid droplets (rBC residuals) were sampled through a counterflow virtual impactor (CVI). Overall, the presence of low-level clouds was associated with a radical change in the concentration and size distribution of rBC particles in the boundary layer compared to the free troposphere. Four flights conducted in the presence of inside-inversion, surface-coupled, mixed-phase clouds over sea ice, were selected to address the variability of rBC particles sampled above, below and within the cloud layer. We show that the properties of rBC such as concentration, size and mixing state drastically changed from the above to the below cloud layers, but also within the cloud layers from cloud top to cloud bottom. Our results might suggest the occurrence of a cloud-mediated transformation cycle of rBC particles in the boundary layer which includes activation, cloud processing, and sub-cloud release of processed rBC agglomerates. In the case of persistent low-level Arctic clouds, this cycle may reiterate multiple times, adding one additional degree of complexity to the understanding of cloud processing of black carbon particles in the Arctic.
... This suggests that instead of residual water, the feature is a shattering artifact from the inlets, or, more likely, is related to how marine aerosols are sized by the UHSAS. Recent work (Kupc et al., 2018;Moore et al., 2021) has demonstrated that SSA, which are expected to have refractive indices much lower than those of the commonly used PSL calibration particles, will be undersized by the UHSAS. When combined with lower response sensitivity at sizes above 500 nm, such unexpected features may appear in the UHSAS distribution. ...
This study focuses on methods to estimate dry marine aerosol surface area (SA) from bulk optical measurements. Aerosol SA is used in many models' ice nucleating particle (INP) parameterizations, as well as influencing particle light scattering, hygroscopic growth, and reactivity, but direct observations are scarce in the Southern Ocean (SO). Two campaigns jointly conducted in austral summer 2018 provided co‐located measurements of aerosol SA from particle size distributions and lidar to evaluate SA estimation methods in this region. Mie theory calculations based on measured size distributions were used to test a proposed approximation for dry aerosol SA, which relies on estimating effective scattering efficiency (Q) as a function of Ångström exponent (å). For distributions with dry å < 1, Q = 2 was found to be a good approximation within ±50%, but for distributions with dry å > 1, an assumption of Q = 3 as in some prior studies underestimates dry aerosol SA by a factor of 2 or more. We propose a new relationship between dry å and Q, which can be used for −0.2 < å < 2, and suggest å = 0.8 as the cutoff between primary and secondary marine aerosol‐dominated distributions. Application of a published methodology to retrieve dry marine aerosol SA from lidar extinction profiles overestimated aerosol SA by a factor of 3–5 during these campaigns. Using Microtops aerosol optical thickness measurements, we derive alternative lidar conversion parameters from our observations, applicable to marine aerosol over the SO.
... Particle composition affects AOD and AE via intrinsic properties such as refractive index and through influences on particle size via changes in hygroscopicity and water uptake. 73,74 Cloudy versus clear sky differences in overall PM 2.5 and ALW mass are sharpest during spring and summer, exhibiting similar patterns to AOD and AE measurements for those categories. In the summer when PM 2.5 and ALW mass are the highest, AOD is also the highest. ...
Particle chemical composition affects aerosol optical and physical properties in ways important for the fate, transport, and impact of atmospheric particulate matter. For example, hygroscopic constituents take up water to increase the physical size of a particle, which can alter the extinction properties and atmospheric lifetime. At the collocated AERosol RObotic NETwork (AERONET) and Interagency Monitoring of PROtected Visual Environments (IMPROVE) network monitoring stations in rural Bondville, Illinois, we employ a novel cloudiness determination method to compare measured aerosol physicochemical properties on predominantly cloudy and clear sky days from 2010 to 2019. On cloudy days, aerosol optical depth (AOD) is significantly higher than on clear sky days in all seasons. Measured Ångström exponents are significantly smaller on cloudy days, indicating physically larger average particle size for the sampled populations in all seasons except winter. Mass concentrations of fine particulate matter that include estimates of aerosol liquid water (ALW) are higher on cloudy days in all seasons but winter. More ALW on cloudy days is consistent with larger particle sizes inferred from Ångström exponent measurements. Aerosol chemical composition that affects hygroscopicity plays a determining impact on cloudy versus clear sky differences in AOD, Ångström exponents, and ALW. This work highlights the need for simultaneous collocated, high-time-resolution measurements of both aerosol chemical and physical properties, in particular at cloudy times when quantitative understanding of tropospheric composition is most uncertain.
... UHSAS sizing uncertainty is within 2.5 % of the particle size (Uin, 2016) with variations of −10 % to +4 % based on calibrated particles with known refractive indices between 1.44 and 1.58 (Moore et al., 2021). The reported systematic uncertainty of the number size concentration for accumulation mode (0.1-1 µm) particles measured by UHSAS has been shown to be 3.9 % due to calibration, flow, and pressure biases (Kupc et al., 2018). This instrument error propagates to −27.5 % to +12.4 % for higher moments of the size distribution, such as surface area and volume (Kupc et al., 2018;Brock et al., 2019). ...
... The reported systematic uncertainty of the number size concentration for accumulation mode (0.1-1 µm) particles measured by UHSAS has been shown to be 3.9 % due to calibration, flow, and pressure biases (Kupc et al., 2018). This instrument error propagates to −27.5 % to +12.4 % for higher moments of the size distribution, such as surface area and volume (Kupc et al., 2018;Brock et al., 2019). We therefore adopted a size uncertainty value (σ D ) of 2.5 % as defined by the UHSAS instrument manufacturer (Uin, 2016), and 10 % for the concentration uncertainty (σ PNSD ), which has been used in previous inversion procedures (Bluvshtein et al., 2017;Frie and Bahreini, 2021). ...
Improved quantification of sea spray aerosol concentration and size is important for determining aerosol effects on clouds and the climate, though attempts to accurately capture the size distribution of the sea spray mode remain limited by the availability of supermicron size distributions. In this work, we introduce a new approach to retrieving lognormal mode fit parameters for a sea spray aerosol mode by combining submicron size distributions with supermicron scattering measurements using a Mie inversion. Submicron size distributions were measured by an ultra-high-sensitivity aerosol spectrometer (UHSAS), and supermicron scattering was taken as the difference between <10 µm and <1 µm three-wavelength integrating nephelometer measurements (NEPH). This UHSAS-NEPH method was applied during background marine periods of the Department of Energy Atmospheric Radiation Measurement Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign on Ascension Island (November 2016–May 2017), when the contribution of sea spray aerosol was expected to represent a large fraction of the aerosol mass and total scattering. Lognormal sea spray modal parameters were retrieved from comparisons between nephelometer measurements and a lookup table of Mie theory-simulated scattering coefficients for low-error solutions that minimized the 0.4–1 µm residual in the UHSAS size distribution. We evaluated the UHSAS-NEPH method with a set of clean marine measurements in the North Atlantic that included supermicron size and chemical measurements, showing that measured supermicron size distributions are needed to constrain the sea spray number concentration but that mass concentration was reasonably characterized using supermicron scattering. For LASIC, the UHSAS-NEPH method retrieved sea spray mode properties for approximately 88 % of the background marine times when the scattering variability and total particle concentration were low (<± 5 Mm−1 and <400 cm−3, respectively), with mass mean diameter ranging from 0.6 to 1.9 µm (1.47 ± 0.17 µm), modal width ranging from 1.1 to 3.97 (2.4±0.3), and mass concentration ranging from 0.18 to 23.0 µg m−3 (8.37. ± 4.1 µg m−3). The measured nephelometer scattering at three wavelengths was found to constrain the mode width marginally at the largest particle sizes in the absence of additional size and chemical measurements for defining parameters for the Mie solutions. Comparing UHSAS-NEPH retrievals to those of a fitting algorithm applied only to the submicron UHSAS number size distribution showed that correlations between retrieved mass concentration and the available mass-based sea spray tracers (coarse scattering, wind speed, and chloride) are low when supermicron measurements are not considered. This work demonstrates the added value of supermicron scattering measurements for retrieving reasonable sea spray mass concentrations, providing the best-available observationally constrained estimate of the sea spray mode properties when supermicron size distribution measurements are not available.
... 37,38 A High-Resolution Aerosol Mass Spectrometer (HR-AMS; Aerodyne Research) measured the mass concentrations and composition of the sub-micron, non-refractory aerosol every 5 seconds. 20 Measurements of aerosol mass concentrations and OA elemental ratios of H : C and O : C from the HR- 71) and these were used to inform the shape of the initial aerosol size distribution (median and geometric standard deviation). We used the 10 seconds merge data for all the measurements mentioned above and conversions were performed when necessary to calculate concentrations at ambient conditions (instead of at standard temperature and pressure conditions). ...
Wildfires are an important atmospheric source of primary organic aerosol (POA) and precursors for secondary organic aerosol (SOA) at regional and global scales. However, there are large uncertainties surrounding the...
... s41561-022-00901-w. Particle diameters were derived from optical spectrometer calibrations using ammonium sulfate, which has a refractive index that is also appropriate for many mineral dusts and most other tropospheric particle types 17,52,54 . Sample flows were 0.06 l min −1 and 0.1 l min −1 , respectively. ...
Airborne mineral dust particles can act as natural seeds for cirrus clouds in the upper troposphere. However, the atmospheric abundance of dust is unconstrained in cirrus-forming regions, hampering our ability to predict these radiatively important clouds. Here we present global-scale measurements of dust aerosol abundance in the upper troposphere and incorporate these into a detailed cirrus-formation model. We show that dust aerosol initiates cirrus clouds throughout the extra-tropics in all seasons and dominates cirrus formation in the Northern Hemisphere (75–93% of clouds seasonally). Using a global transport model with improved dust treatment, we also explore which of Earth’s deserts are the largest contributors of dust aerosol to cirrus-forming regions. We find that the meteorological environment downstream of each emission region modulates dust atmospheric lifetime and transport efficiency to the upper troposphere so that source contributions are disproportionate to emissions. Our findings establish the critical role of dust in Earth’s climate system through the formation of cirrus clouds. Cirrus cloud formation in the Northern Hemisphere is primarily triggered by mineral dust, according to global-scale dust observations and a cirrus-formation model.
