Ewan Crosbie PhD. Public Presentation

Atmospheric aerosols and trace gases are a highly relevant component of the
climate system affecting atmospheric radiative transfer and the hydrologic
cycle.  In arid and semi-arid regions, where cloud cover is often low and
precipitation is generally scarce and sporadic, the driving processes accounting
for the production, loss and transport of atmospheric constituents are often
distinctly different from other climates.   In arid regions, the same
circulation dynamics that suppress cloud formation can be responsible for
creating strong subsidence inversions, which cap atmospheric mixing and trap
pollutants close to the surface, often placing populated arid regions high on
global rankings of air pollution concerns.  In addition, low soil moisture can
encourage wind-blown dust emissions, which can be a significant fraction of the
total aerosol loading in both coarse and fine modes on a mass basis.

Three distinct focus regions are investigated over varying time scales, using a
diverse set of techniques, and with wide-ranging primary goals.  1) the Tehran
metropolitan area in Iran over a ten-year period from 2000-2009, 2) Tucson,
Arizona over 2011-2014 with three intensive monitoring periods during summer
2014 and winter 2015 and 3) the San Joaquin Valley in California during the NASA
DISCOVER-AQ campaign during Jan-Feb 2013.  However, in all cases, the role of
local and regional scale meteorology plays a significant role in controlling the
spatiotemporal variability in trace gas and aerosol concentrations. Particular
emphasis is placed on understanding transport pathways due to the local wind
patterns and the importance of key meteorological parameters such as
temperature, humidity and solar radiation on controlling production and loss
mechanisms.  While low in magnitude, the precipitation pattern is still an
important sink mechanism that modulates gas phase and particle abundances in all
three regions, either through scavenging or by promoting vertical mixing.

The reported measurements and data analysis serve to improve the
characterization of trace gases and aerosols in populated arid regions and offer
process level understanding of dominant mechanisms for model validations and
improvements.