Gas-Phase CO₂ Subtraction for Improved Measurements of the Organic Aerosol Mass Concentration and Oxidation Degree by an Aerosol Mass Spectrometer

The Aerodyne aerosol mass spectrometer (AMS) has been widely used for real-time characterization of the size-resolved chemical composition of sub-micrometer aerosol particles. The first step in AMS sampling is the pre-concentration of aerosols while stripping away the gas-phase components, which contributes to the high sensitivity of this instrument. The strength of the instrument lies in particle phase measurement; however, ion signals generated from gas-phase species can influence the interpretation of the particle-phase chemistry data. Here, we present methods for subtracting the varying contributions of gas-phase carbon dioxide (CO₂) in the AMS spectra of aerosol particles, which is critical for determining the mass concentration and oxygen-to-carbon (O/C) ratio of organic aerosol. This report gives details on the gaseous CO₂ subtraction analysis performed on a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) data set acquired from sampling of fresh and diluted vehicle emissions. Three different methods were used: (1) collocated continuous gas-phase CO₂ measurement coupled with periodic filter tests consisting of sampling the same particle-free air by the AMS and the CO₂ analyzer, (2) positive matrix factorization (PMF) analysis to separate the gas- and particle-phase signals of CO₂⁺ at <i>m</i>/<i>z</i> 44, and (3) use of the particle time-of-flight (PTOF) size-resolved chemical information for separation of gas- and particle-phase signals at <i>m</i>/<i>z</i> 44. Our results indicate that these three different approaches yield internally consistent values for the gas/particle apportionment of <i>m</i>/<i>z</i> 44, but methods 2 and 3 require certain conditions to be met to yield reliable results. The methods presented are applicable to any situation where gas-phase components may influence the PM signal of interest

Reddening, emission-line, and intrinsic absorption properties in the Narrow-Line Seyfert 1 Galaxy Arakelian 564

We use Hubble Space Telescope UV and optical spectra of the narrow-line Seyfert 1 (NLS1) galaxy Ark 564 to investigate its internal reddening and properties of its emission-line and intrinsic UV absorption gas. We find that the extinction curve of Ark 564, derived from a comparison of its UV/optical continuum to that of an unreddened NLS1, lacks a 2200 Å bump and turns up toward the UV at a longer wavelength (4000 Å) than the standard Galactic, LMC, and SMC curves. However, it does not show the extremely steep rise to 1200 Å that characterizes the extinction curve of the Seyfert 1 galaxy NGC 3227. The emission lines and continuum experience the same amount of reddening, indicating the presence of a dust screen that is external to the narrow-line region. Echelle spectra from the Space Telescope Imaging Spectrograph show intrinsic UV absorption lines due to Lyα, N V, C IV, Si IV, and Si III, centered at a radial velocity of -190 km s-1 (relative to the host galaxy). Photoionization models of the UV absorber indicate that it has a sufficient column (NH = 1.6 × 1021 cm-2) and is at a sufficient distance from the nucleus (D > 95 pc) to be the source of the dust screen. Thus, Ark 564 contains a dusty "lukewarm absorber" similar to that seen in NGC 3227

Biodiversity of the Sebangau tropical peat swamp forest, Indonesian Borneo

The importance of Southeast Asia’s tropical peat swamp forests for biodiversity is becoming increasingly recognised. Information on species presence within peatland areas is scant, however, limiting our ability to develop species conservation strategies and monitor responses to human activities. We compile species presence records for the Sebangau forest in Indonesian Borneo since 1993 and present the most complete Bornean PSF biodiversity inventory yet published. Including morpho-species that are likely to represent true species, this list comprises 215 tree, 92 non-tree flora, 73 ant, 66 butterfly, 297 spider, 41 dragon/damselfly, 55 fish, 11 amphibian, 46 reptile, 172 bird and 65 mammal taxa. Of these, 46 species are globally threatened and 59 are currently protected in Indonesia; 22 vertebrate species are Borneo endemics. Because our sampling is both biased and incomplete, the true number of species found at this site is likely to be much higher. Little is known about many of these taxa in Sebangau and peat swamp forests elsewhere. Many of these species are considered forest dependent, and the entire community is expected to be important for maintaining the resilience of the peat swamp forest ecosystem and the environmental services that it provides. This highlights the need for urgent conservation of Sebangau and its diverse biological community