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  • Author or Editor: R. S. McKenzie x
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W. R. Barchet
and
R. S. McKenzie

Abstract

There are requirements for a laboratory source of pure silver iodide aerosol with long-term output stability. Aerosol generation by a power-coated hot wire is unsatisfactory. A method of filament preparation providing a uniform, tightly bound layer of silver iodide on a nichrome heating filament is presented. Size, condensation activity, and ice nucleation properties of silver iodide particles produced by a plated filament meet laboratory needs. Long-term stability of aerosol output is an important added benefit.

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S. E. Nichol
,
G. Pfister
,
G. E. Bodeker
,
R. L. McKenzie
,
S. W. Wood
, and
G. Bernhard

Abstract

To gauge the impact of clouds on erythemal (sunburn causing) UV irradiances under different surface albedo conditions, UV measurements from two Antarctic sites (McMurdo and South Pole Stations) and a midlatitude site (Lauder, New Zealand) are examined. The surface albedo at South Pole remains high throughout the year, at McMurdo it has a strong annual cycle, and at Lauder it is low throughout the year. The measurements at each site are divided into clear and cloudy subsets and are compared with modeled clear-sky irradiances to assess the attenuation of UV by clouds. A radiative transfer model is also used to interpret the observations. Results show increasing attenuation of UV with increasing cloud optical depth, but a high surface albedo can moderate this attenuation as a result of multiple scattering between the surface and cloud base. This effect is of particular importance at high latitudes where snow may be present during the summer months. There is also a tendency toward greater cloud attenuation with increasing solar zenith angle.

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C. P. Weaver
,
X.-Z. Liang
,
J. Zhu
,
P. J. Adams
,
P. Amar
,
J. Avise
,
M. Caughey
,
J. Chen
,
R. C. Cohen
,
E. Cooter
,
J. P. Dawson
,
R. Gilliam
,
A. Gilliland
,
A. H. Goldstein
,
A. Grambsch
,
D. Grano
,
A. Guenther
,
W. I. Gustafson
,
R. A. Harley
,
S. He
,
B. Hemming
,
C. Hogrefe
,
H.-C. Huang
,
S. W. Hunt
,
D.J. Jacob
,
P. L. Kinney
,
K. Kunkel
,
J.-F. Lamarque
,
B. Lamb
,
N. K. Larkin
,
L. R. Leung
,
K.-J. Liao
,
J.-T. Lin
,
B. H. Lynn
,
K. Manomaiphiboon
,
C. Mass
,
D. McKenzie
,
L. J. Mickley
,
S. M. O'neill
,
C. Nolte
,
S. N. Pandis
,
P. N. Racherla
,
C. Rosenzweig
,
A. G. Russell
,
E. Salathé
,
A. L. Steiner
,
E. Tagaris
,
Z. Tao
,
S. Tonse
,
C. Wiedinmyer
,
A. Williams
,
D. A. Winner
,
J.-H. Woo
,
S. WU
, and
D. J. Wuebbles

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the different groups, simulated global climate change causes increases of a few to several parts per billion (ppb) in summertime mean maximum daily 8-h average O3 concentrations over substantial regions of the country. The different modeling experiments in general do not, however, simulate the same regional patterns of change. These differences seem to result largely from variations in the simulated patterns of changes in key meteorological drivers, such as temperature and surface insolation. How isoprene nitrate chemistry is represented in the different modeling systems is an additional critical factor in the simulated O3 response to climate change.

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