Jamie H. Lyons

Airborne measurements of particle and gas emissions from the 1990 volcanic eruptions of Mount Redoubt

Airborne in situ and remote sensing (lidar and correlation spectrometer) measurements are described for the volcanic emissions from Mount Redoubt, Alaska, in January and June 1990. The lidar provided excellent real-time information on the distribution of the volcanic effluents. In postanalysis the lidar observations were used to determine cross-sectional areas of the plumes of emissions which, together with the airborne in situ measurements, were used to derive the fluxes of particles and gases from the volcano. For the intraeruptive emissions the ranges of the derived fluxes were for water vapor, ∼160–9440 kg s−1; for CO2, ∼30–1710 kg s−1; for SO2, ∼1–140 kg s−1; for particles (<48 μm diameter), ∼1–6 kg s−1; for SO4=, <0.1–2 kg s−1; for HCl, <0.01–2 kg s−1; and for NOx, <0.1–2 kg s−1;. Independent measurements of SO2 from a correlation spectrometer during the period of active dome growth between late March and early June 1990 gave fluxes from 12 to 75 kg s−1;. The particles in the intraeruptive emissions consisted primarily of silicate rock and mineral fragments devoid of any sulfuric acid coating. Very little of the SO2 (∼0.1%) was oxidized to sulfate in the cold, dark conditions of the Arctic atmosphere. During a large eruption of Mount Redoubt on January 8, 1990, the particle (<48 μm diameter) emission flux averaged ∼104 kg s−1. During posteruptive emissions on June 11, 1990, the fluxes of both particles and gases were either close to or less than our lower detection limits (except for water vapor, which had a flux of ∼6×103 kg s−1).

Arctic hazes in summer over Greenland and the North American Arctic. I: Incidence and origins

Airborne observations during August 1985 over Greenland and the North American Arctic revealed that dense, discrete haze layers were common above 850 mb. No such hazes were found near the surface in areas remote from local sources of particles. The haze layers aloft were characterized by large light-scattering coefficients due to dry particles (maximum value 1.24 × 10−4m−1) and relatively high total particle concentrations (maximum value 3100 cm−3). Sulfate was the dominant ionic component of the aerosol (0.06 – 1.9 μg m−3); carbon soot was also present. Evidence for relatively fresh aerosols, accompanied by NO2 and O3 depletion, was found near, but not within, the haze layers. The hazes probably derived from anthropogenic sources and/or biomass burning at midlatitudes.It is hypothesized that the scavenging of particles by stratus clouds plays an important role in reducing the frequency and intensity of hazes at the surface in the Arctic in summer. Since the detection of haze layers aloft through measurements of column-integrated parameters from the surface (e.g., by lidar) cannot be carried out reliably when clouds are present, such measurements have likely underestimated the occurrence of haze layers in the Arctic, particularly in summer.

Aerosol and lidar measurements of hazes in mid-latitude and polar airmasses

Abstract Airborne lidar and in situ measurements of hazes were obtained in March 1986 during research flights from the East Coast of the United States to Baffin Island, Canada. Mid-latitude and polar airmasses, clearly separated by a frontal zone, displayed distinct differences in aerosol characteristics and in the vertical structure of aerosol layers. The data illustrate the differences between freshly polluted, mid-latitude air and clean and hazy polar air. Particle size spectra in the mid-latitude airmass contained distinct nucleation (0.01–0.1 μm diameter) and accumulation (0.1–1.0 μm diameter) modes, while in the polar airmass there was generally only an accumulation mode. The modal diameter of particles in the accumulation mode increased with increasing particle concentration in the polar airmass. Differences in the shapes of the particle size spectra measured in the two airmasses can be explained by differences in the sources and lifetimes of the particles. Hazes observed by a 1.064 μm wavelength lidar in the mid-latitude airmass were relatively diffuse, while those in the polar airmass appeared in multiple thin laminae. Measurements of the wind speed profile suggest that the multi-layered structure of the hazes in the polar airmass was due to the advection of thin, hazy regions into the generally clean polar airmass and by the extreme thermal stability of the lower troposphere.

Field studies of a power plant plume in the arid southwestern United States

Abstract A study is presented of the physics and chemistry relevant to the visual impact of the plume from an electric power generating plant located in the Mojave Desert. The amount of light absorption by particles in the plume did not differ significantly from that by particles in the ambient air. While sulfate and nitrate occasionally contributed substantially to the total particle mass in the plume, generally they contributed −1 for sulfate and ∼ 0.08% h −1 for nitrate. Light scattering by the plume was more dependent on the total mass of particles in the sub-μm size range than on sulfate mass alone. At a wavelength of 550 nm, NO 2 absorption frequently contributed about equally with light scattering particles to the optical depth of the plume.

Radar Detection of Cloud-Seeding Effects

The effects on precipitation of artificially seeding clouds with Dry Ice have been monitored from cloud to ground with a radar that has a wavelength of 8.6 millimeters.

Background particle size distributions over North America

The data presented in this paper demonstrate that very clean air, generally considered to be confined to remote oceanic regions, is not uncommon deep in the interiors of the North American continent.