2011 - Cooperative Institute for Research in Environmental Sciences ...

Complete analysis of the three completed HIAPER
(High-Altitude Instrumented Airborne Platform for Environmental
Research) Pole-to-Pole Observations (HIPPO)
deployments was presented at the American Geophysical
Union Fall Meeting in 2010. The results suggest that these
measurements can be used to provide a single “typical remote”
black carbon (BC) mass distribution for comparison
to global models. Additionally, even in very different remote
air masses, the estimated impact on BC absorption of
shortwave solar radiation by dry coatings on BC cores was
found to be fairly uniform, and to lie in good agreement
with previous lower-stratospheric results. In the exceptionally
clean Southern Hemisphere, measurements made
in the third HIPPO deployment revealed two populations
of BC-containing aerosol distinguished by the amount of
dry coatings associated with the BC cores. This observation
may provide a strong constraint on the absolute and
relative aging of BC-containing aerosol and its transport
timescales in global models.
At present a manuscript presenting these analyses and
results is in preparation for publication in Geophysical
Research Letters.
J. P. SCHWARZ
The NSF/NCAR GV research aircraft used for the HIPPO mission with a
backdrop of the mountains of American Samoa.
Milestone 2. Examine organosulfate molecules in atmospheric
aerosols. Impact: Organosulfate molecules
can be formed when reaction products of isoprene and
other biogenic organic products encounter acidic sulfate
particles. Laboratory calibrations and a review of more
than 10 years of field data will allow an assessment of the
importance of these compounds in many atmospheric
situations, including the Amazon boundary layer and the
free troposphere over the United States.
Organosulfate compounds have recently been identified
within aerosol particles in laboratory smog chamber studies.
Organosulfate compounds form when isoprene oxidation
products react with acidic sulfate aerosol particles.
Gas-phase isoprene emitted from broadleaf vegetation
constitutes an enormous flux of organic material into the
atmosphere, and converting a small fraction of this emitted
mass to condensed phase species would add dramatically
to atmospheric aerosol loadings. Isoprene-derived
organosulfates have not been previously observed in the
real atmosphere.
For this project, organosulfate compounds were detected
in free tropospheric aerosol by an airborne single particle
mass spectrometer instrument. Laboratory calibrations
enabled estimations of organosulfate aerosol mass loadings
for a variety of atmospheric regions including the
Arctic, continental midlatitudes and the tropics. Organo-
sulfate loadings were highest in tropical and midlatitude
air masses situated downwind of strong isoprene sources
such as the Amazon and the southeastern U.S., where
isoprene-derived organosulfates contributed from 1-20%
of total aerosol mass regionally. This research provides
new evidence on how urban and industrial emissions of
sulfur compounds combine with typical biogenic emissions
to generate substantial aerosol mass on regional and
global scales. These results were published in the Proceedings
of the National Academy of Science and presented at the
American Association for Aerosol Research and American
Geophysical Union annual meetings.
Milestone 3. Use data from the 2010 CalNex Air Quality
Study to investigate secondary organic aerosol (SOA) formation
in the urban Los Angeles area. Impact: This CIRES
research will enable us to quantify the anthropogenic
source of SOA to the atmosphere, which is currently not
well understood. By combining the results from multiple
measurements, we will investigate how the budget of
organic carbon in the gas and aerosol phases changes as a
function of the degree of photochemical processing. The
results will be used to estimate the global source of SOA
derived from anthropogenic volatile organic compounds
and other urban precursors.
Work has started on the analysis of gas- and aerosolphase
organic carbon species obtained during the Cal-
Nex (Research at the Nexus of Air Quality and Climate
Change) field study in 2010, with a special focus on the
production of secondary organic aerosol (SOA). Initial
analyses focused on the emissions characterization of
volatile organic compounds, the chemical formation
of glyoxal and other reaction intermediates and on the
weekend-weekday effect in the production of SOA. First
results were presented at the CalNex workshop in Sacramento,
Calif., in May 2011. A detailed analysis of glyoxal
measurements made at the ground site in Pasadena, Calif.,
was performed with the help of box-model calculations,
and the manuscript is currently under review. This study
found that the production of several reaction intermedi-
CIRES Annual Report 2011 131