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Molecular and physical characteristics of aerosol at a remote free troposphere site
Simeon K. Schum, Bo Zhang, Katja Džepina, Paulo Fialho, Claudio Mazzoleni, Lynn R. Mazzoleni, 2018, izvirni znanstveni članek

Opis: Aerosol properties are transformed by atmospheric processes during long-range transport and play a key role in the Earth’s radiative balance. To understand the molecular and physical characteristics of free tropospheric aerosol, we studied samples collected at the Pico Mountain Observatory in the North Atlantic. The observatory is located in the marine free troposphere at 2225m above sea level, on Pico Island in the Azores archipelago. The site is ideal for the study of long-range-transported free tropospheric aerosol with minimal local influence. Three aerosol samples with elevated organic carbon concentrations were selected for detailed analysis. FLEXPART retroplumes indicated that two of the samples were influenced by North American wildfire emissions transported in the free troposphere and one by North American outflow mainly transported within the marine boundary layer. Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry was used to determine the detailed molecular composition of the samples. Thousands of molecular formulas were assigned to each of the individual samples. On average  60% of the molecular formulas contained only carbon, hydrogen, and oxygen atoms (CHO),  30% contained nitrogen (CHNO), and  10% contained sulfur (CHOS). The molecular formula compositions of the two wildfire-influenced aerosol samples transported mainly in the free troposphere had relatively low average O=C ratios (0:480:13 and 0:450:11) despite the 7–10 days of transport time according to FLEXPART. In contrast, the molecular composition of the North American outflow transported mainly in the boundary layer had a higher average O=C ratio (0:570:17) with 3 days of transport time. To better understand the difference between free tropospheric transport and boundary layer transport, the meteorological conditions along the FLEXPART simulated transport pathways were extracted from the Global Forecast System analysis for the model grids. We used the extracted meteorological conditions and the observed molecular chemistry to predict the relative-humidity-dependent glass transition temperatures (Tg) of the aerosol components. Comparisons of the Tg to the ambient temperature indicated that a majority of the organic aerosol components transported in the free troposphere were more viscous and therefore less susceptible to oxidation than the organic aerosol components transported in the boundary layer. Although the number of observations is limited, the results suggest that biomass burning organic aerosol injected into the free troposphere is more persistent than organic aerosol in the boundary layer having broader implications for aerosol aging.
Najdeno v: osebi
Ključne besede: secondary organic aerosols, brown carbon, particle dispersion model, ultrahigh-resolution FT-ICR MS, Pico Mountain Observatory
Objavljeno: 10.04.2021; Ogledov: 247; Prenosov: 0
.pdf Polno besedilo (5,35 MB)

Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean
Claudio Mazzoleni, Katja Džepina, Kendra Wright, R. Chris Owen, Paulo Fialho, Lynn R. Mazzoleni, Swarup China, Peter A. Alpert, Bo Zhang, Simeon K. Schum, 2017, izvirni znanstveni članek

Opis: Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition between samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity (RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. This study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formation.
Najdeno v: osebi
Ključne besede: atmospheric aerosols, ice nucleating particles, long-range transport, optical microscopy, electron microscopy, Pico Mountain Observatory
Objavljeno: 11.04.2021; Ogledov: 287; Prenosov: 13
URL Polno besedilo (0,00 KB)
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