Evolution of Pinatubo aerosol near 19 km altitude over western North America

Abstract

Stratospheric aerosols, collected near 19 km altitude on wire impactors over western North America from August 20, 1991 to May 11, 1993, show strong influence of the June 1991 Mt. Pinatubo eruption. Lognormal size distributions are bimodal; each of the mode radii increases and reaches maximum value at about 15 months after eruption. The second (large particle) mode becomes well developed then, and about 40% of the droplets are larger than 0.4 µm radius. The eruption of Mt. Spurr (Alaska) may also have contributed to this. Sulfate mass loading decays exponentially (e‐folding 216 days), similar to El Chichon. Silicates are present in samples only immediately after eruption. Two years after eruption, sulfate mass loading is about 0.4 µg/m³, about an order of magnitude higher than background pre‐volcanic values. Aerosol size distributions are still bimodal with a very well‐defined large droplet mode.

A review of stratospheric aerosol characterization

“…Within a bin, the profiles have an uncertainty dominated by the statistical variability. Secondly, the assumption of monomodality introduces a bias, that was however appreciably reduced by applying a correction factor estimated from available in situ measurements (Pueschel et al, 1992Goodman et al, 1994;Deshler and Oltmans, 1998). Furthermore, the uncertainty on the aerosol composition greatly affects the error, especially in the IR mode, as already discussed.…”

“…In this respect, lidar networks such as the European lidar network EARLINET , or the Wyoming data set spread over about 30 years constitute precious data sources that are extensively used for validation of data derived from remote sensing measurements. This is also the case of data collections from various in situ campaigns as those presented in Goodman et al (1994), Pueschel et al (1994). Bauman's efforts to collect data from various in situ experiments in order to improve the retrieval of aerosol parameters (Bauman et al, 2003a) illustrates very well the interest of such a process, but also the difficulty to collect a representative data set in time and space.…”

“…In situ measurements by airborne or balloonborne optical particle counting Sugita et al, 1999), wire impactors (Sheridan et al, 1992;Goodman et al, 1994;Pueschel et al, 1994) or spectrometers Renard et al, 2002) give direct measurements with a high vertical resolution of local microphysical aerosol properties, such as the shape, size distribution and composition. Their ability to discriminate a wide range of particles, from condensation nuclei (size $0.1 lm) to large aerosol droplets (size $1 lm) makes possible a reliable determination of the size distribution, included in the case of multimodal size distributions.…”

“…Pueschel et al (1994) mentions the problem of evaporation by adiabatic heating of air in the entrance of the impactor, leading to particle losses and to an underestimation of the particle radius. Finally, wire-impactors generally underestimate the particle number with respect to dust sondes, optical filters and laser optical probes (Goodman et al, 1994).…”

Comparison of lidar measurement with balloonborne OPC measurement over Bandung, Indonesia

“…In this work we use a lognormal size distribution function, which is most commonly used (e.g. 8,9,10). This function form is given by (1) where n(r) is the differential concentration in the radius interval dr, k is the number of modes in the distribution, N is the total particle number concentration, r is the median radius, cr is the distribution width for each i-th mode.…”