Development of balloon-borne impactor payload for profiling free tropospheric aerosol

Size-segregated aerosol vertical profiles in the troposphere are critically important for source attribution, transformation processes, atmospheric stability, and radiative forcing. For the first time, the development of a 6-stage impactor for real-time balloon-borne measurements of size-segregated (cutoff diameter [Dae]: 0.15–5 µm) aerosol mass concentrations in the free troposphere was tested during spring 2016 over Hyderabad, India, is presented. Total aerosol mass concentrations obtained with the 6-stage impactor (MTI) and a co-located optical particle counter (MTOPC) measurements at the surface under ambient conditions agreed to within 15%. The effect of aerosol particle growth on the MTI data are assessed using an urban aerosol particle model by scaling mass concentration of water-soluble (hydrophilic) aerosol particles at ambient relative humidity (RH) to that at RH = 50%. An overall uncertainty of the measurement of the MTI was estimated to be about 19%. The altitude variation of size-segregated mass concentrations of aerosol particles along with thermodynamic variables depicted convectively well-mixed layer extending up to about 4.5 km within which aerosol particles showed two distinct layers, one at ∼2 km and another at about 4.5 km. The size-resolved air samples containing aerosol particles collected using the balloon-borne 6-stage impactor will be useful for their chemical characterization and also long-range transport studies. Copyright © 2019 American Association for Aerosol Research</p

Mass absorption cross section of black carbon for Aethalometer in the Arctic

Long-term measurements of the mass concentration of black carbon (BC) in the atmosphere (MBC) with well-constrained accuracy are indispensable to quantify its emission, transport, and deposition. The aerosol light absorption coefficient (babs), usually measured by a filter-based absorption photometer, including an Aethalometer (AE), is often used to estimate MBC. The measured babs is converted to MBC by assuming a value for the mass absorption cross section (MAC). Previously, we derived the MAC for AE (MAC (AE)) from measured babs and independently measured MBC values at two sites in the Arctic. MBC was measured with a filter-based absorption photometer with a heated inlet (COSMOS). The accuracy of the COSMOS-derived MBC (MBC (COSMOS)) was within about 15%. Here, we obtained additional MAC (AE) measurements to improve understanding of its variability and uncertainty. We measured babs (AE) and MBC (COSMOS) at Alert (2018–2020), Barrow (2012–2022), Ny-Ålesund (2012–2019), and Pallas (2019–2022). At Pallas, we also obtained four-wavelength photoacoustic aerosol absorption spectrometer (PAAS-4λ) measurements of babs. babs (AE) and MBC (COSMOS) were tightly correlated; the average MAC (AE) at the four sites was 11.4 ± 1.2 m2 g−1 (mean ± 1σ) at 590 nm and 7.76 ± 0.73 m2 g−1 at 880 nm. The spatial variability of MAC (AE) was about 11% (1σ), and its year-to-year variability was about 18%. We compared MAC (AE) in the Arctic with values at mid-latitudes, measured by previous studies, and with values obtained by using other types of filter-based absorption photometer, and PAAS-4λ. Copyright © 2024 American Association for Aerosol Research</p