ALBERT

Beschreibung: Emissions from 15 agricultural fires in the southeastern US were measured from the NASA DC-8 research aircraft during the summer 2013 SEAC 4 RS campaign. This study reports a detailed set of emission factors (EFs) for 25 trace gases and 6 fine particle species. The chemical evolution of the primary emissions in 7 plumes was examined in detail for ~1.2 hr. A Lagrangian plume cross-section model was used to simulate the evolution of ozone (O 3 ), reactive nitrogen species, and organic aerosol (OA). Observed EFs are generally consistent with previous measurements of crop residue burning, but the fires studied here emitted high amounts of SO 2 and fine particles, especially primary OA and chloride. Filter-based measurements of aerosol light absorption implied that brown carbon (BrC) was ubiquitous in the plumes. In aged plumes, rapid production of O 3 , peroxyacetyl nitrate (PAN), and nitrate were observed with ΔO 3 /ΔCO, ΔPAN/ΔNO y , and Δnitrate/ΔNO y reaching ~0.1, ~0.3, and ~0.3. For 5 selected cases, the model reasonably simulated O 3 formation but underestimated PAN formation. No significant evolution of OA mass or BrC absorption was observed. However, a consistent increase in oxygen-to-carbon (O/C) ratios of OA indicated that OA oxidation in the agricultural fire plumes was much faster than in urban and forest fire plumes. Finally, total annual SO 2 , NO x , and CO emissions from agricultural fires in Arkansas, Louisiana, Mississippi, and Missouri were estimated (within a factor of ~2) to be equivalent to ~2% SO 2 from coal combustion and ~1% NO x and ~9% CO from mobile sources.

Beschreibung: Meteorology and microphysics affect cloud formation, cloud droplet distributions and shortwave reflectance. The Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) and the Stratocumulus Observations of Los-Angeles Emissions Derived Aerosol-Droplets (SOLEDAD) studies provided measurements in six case studies of cloud thermodynamic properties, initial particle number distribution and composition, and cloud drop distribution. In this study, we use simulations from a chemical and microphysical aerosol-cloud parcel (ACP) model with explicit kinetic drop activation to reproduce observed cloud droplet distributions of the case studies. Four cases had sub-adiabatic lapse rates, resulting in fewer activated droplets, lower liquid water content (LWC) and higher cloud base height than an adiabatic lapse rate. A weighted ensemble of simulations that reflect measured variation in updraft velocity and cloud base height was used to reproduce observed droplet distributions. Simulations show organic hygroscopicity in internally mixed cases causes small effects on cloud reflectivity (CR) (〈0.01), except for cargo ship and smoke plumes, which increased CR by 0.02 and 0.07, respectively, owing to their high organic mass fraction. Organic hygroscopicity had larger effects on droplet concentrations for cases with higher aerosol concentrations near the critical diameter (namely polluted cases with a modal peak near 0.1 µm). Differences in simulated droplet spectral widths (k) caused larger differences in CR than organic hygroscopicity in cases with organic mass fractions of 60% or less for the cases shown. Finally, simulations from a numerical parameterization of cloud droplet activation suitable for GCMs compared well with the ACP model, except under high organic mass fraction.

Beschreibung: The distribution of isotopes within O 2 molecules can be rapidly altered when they react with atomic oxygen. This mechanism is globally important: while other contributions to the global budget of O 2 impart isotopic signatures, the O( 3 P ) + O 2 reaction resets all such signatures in the atmosphere on sub-decadal timescales. Consequently, the isotopic distribution within O 2 is determined by O 3 photochemistry and the circulation patterns that control where that photochemistry occurs. The variability of isotopic ordering in O 2 has not been established, however. We present new measurements of 18 O 18 O in air (reported as Δ 36 values) from the surface to 33 km altitude. They confirm the basic features of the clumped-isotope budget of O 2 : Stratospheric air has higher Δ 36 values than tropospheric air (i.e., more 18 O 18 O), reflecting colder temperatures and fast photochemical cycling of O 3 . Lower Δ 36 values in the troposphere arise from photochemistry at warmer temperatures balanced by the influx of high-Δ 36 air from the stratosphere. These observations agree with predictions derived from the GEOS-Chem chemical transport model, which provides additional insight. We find a link between tropical circulation patterns and regions where Δ 36 values are reset in the troposphere. The dynamics of these regions influences lapse rates, vertical and horizontal patterns of O 2 reordering, and thus the isotopic distribution toward which O 2 is driven in the troposphere. Temporal variations in Δ 36 values at the surface should therefore reflect changes in tropospheric temperatures, photochemistry, and circulation. Our results suggest that the tropospheric O 3 burden has remained within a ±10% range since 1978.

Beschreibung: A chemical ionization mass spectrometer (CIMS) was used to measure BrO and HOBr + Br 2 over the Tropical West Pacific Ocean within the altitude range of 1 to 15 km, during the CONvective TRansport of Active Species in the Tropics (CONTRAST) campaign in 2014. Isolated episodes of elevated BrO (up to 6.6 pptv) and/or HOBr + Br 2 (up to 7.3 pptv) were observed in the tropical free troposphere (TFT) and were associated with biomass burning. However, most of the time we did not observe significant BrO or HOBr + Br 2 in the TFT and the tropical tropopause layer (TTL) above our limits of detection (LOD). The 1-min average LOD for BrO ranged from 0.6 to 1.6 pptv, and for HOBr + Br 2 ranged from 1.3 to 3.5 pptv. During one flight, BrO observations from the TTL to the extratropical lowermost stratosphere (LMS) were used to infer a profile of inorganic bromine (Br y ). Based on this profile, we estimated the product gas injection (PGI) of bromine species into the stratosphere to be 2 pptv. Analysis of Br y partitioning further indicates that BrO levels are likely very low in the TFT environment, and that future studies should target the measurement of HBr or atomic Br.

Beschreibung: Spatial and high-time-resolution properties of the velocities, magnetic field, and 3D electric field within plasma turbulence are examined observationally using data from the Magnetospheric Multiscale Mission. Observations from a Kelvin-Helmholtz instability (KHI) on the Earth's magnetopause are examined, which both provides a series of repeatable intervals to analyze, giving better statistics, and provides a first look at the properties of turbulence in the KHI. For the first time direct observations of both the high-frequency ion and electron velocity spectra are examined, showing differing ion and electron behavior at kinetic scales. Temporal spectra exhibit power law behavior with changes in slope near the ion gyrofrequency and lower-hybrid frequency. The work provides the first observational evidence for turbulent intermittency and anisotropy consistent with quasi-two-dimensional turbulence in association with the KHI. The behavior of kinetic scale intermittency is found to have differences from previous studies of solar wind turbulence, leading to novel insights on the turbulent dynamics in the KHI.