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

A comparison of simulations where anthropogenic
emissions are kept constant was also investigated. It was
found that the magnitude of the emission-driven trends
exceeds the natural variability for the chemical compounds
considered in the study. It can, therefore, be concluded that
emission-management strategies have had a significant
impact over the past 10 years, hence supporting further
emission-reductions strategies. Simulations for the 2010-
2030 period are currently under way, using different sets of
emissions scenarios, based on the emissions provided by
the RCPs.
Product: Colette, A, C Granier, O Hodnebrog, H Jakobs, A
Maurizi, A Nyiri, B Bessagnet, A D’Angiola, M D’Isidoro,
M Gauss, F Meleux, M Memmesheimer, A Mieville, L
Rouïl, F Russo, S Solberg, F Stordal, and F Tampieri, submitted
to Atmos. Chem. Phys.
CSD-13KineticsandPhotochemicalStudies
FEDERAL LEAD: JIM BURKHOLDER
CIRES LEAD: CHRISTINE ENNIS
NOAA Goal 2: Climate
Project Goal: Determine the rates of climate-relevant processes
and evaluate the lifetimes and radiative properties
of atmospheric species (gases and particles) that influence
climate.
Milestone 1. Measure rate coefficients for the chlorine
monoxide self reaction (ClO + ClO + M) over a range of
temperatures and pressures relevant to polar stratospheric
photochemistry. Impact: This research will provide data
needed to reduce uncertainties in atmospheric model
calculations of polar ozone loss. This research has implications
for stratospheric ozone chemistry and climatechemistry
coupling.
Halogen chemistry plays an important role in polar
stratospheric ozone loss. The ClO dimer (ClOOCl) catalytic
ozone destruction cycle accounts for the vast majority of
winter/spring polar stratospheric ozone loss. A key step
in the dimer catalytic cycle is the pressure- and temperature-dependent
self-reaction of the ClO radical. The rate
coefficient for the ClO self-reaction has been measured
in previous laboratory studies but uncertainties persist,
particularly at atmospherically relevant temperatures and
pressures. In this laboratory study, rate coefficients for the
ClO self-reaction were measured over a range of temperatures
(200–296 K) and pressures (50–600 Torr, He and N2
bath gases). ClO radicals were produced by pulsed laser
photolysis of Cl2O at 248 nm. The ClO radical temporal
profile was measured using dual wavelength cavity ringdown
spectroscopy (CRDS) near 280 nm. The absolute ClO
radical concentration was determined using the ClO UV
absorption cross sections, and their temperature dependence
was measured as part of this work. The results from
this work are in conflict with several previous studies that
form the basis of current kinetic recommendations for use
in atmospheric models. The impact of these differences on
polar stratospheric chemistry and ozone loss will be evaluated
in future work.
Milestone 2. Measure ultraviolet (UV) absorption cross
sections of the long-lived ozone-sepleting and greenhouse
gases nitrous oxide (N2O) and carbon tetrachloride
(CCl4) as a function of temperature. Impact: UV photolysis
is the key atmospheric loss process for these compounds.
The laboratory data will be used as input for atmospheric
models to better define the impact of these trace gases on
stratospheric ozone and climate change.
The long-lived atmospheric species nitrous oxide (N2O)
and carbon tetrachloride (CCl4) are ozone-depleting substances
and potent radiative forcing agents. The abundance
and atmospheric lifetimes of N2O and CCl4 are, therefore,
important to understanding stratospheric ozone recovery
and climate change as well as the linkage between these issues.
This study measured properties of N2O and CCl4 that
are key to determining the lifetime of these gases in the
atmosphere. Absorption cross sections were measured at
five atomic UV lines (ranging from 184.95 nm to 228.8 nm)
at temperatures in the range of 210–350 K. In addition, UV
absorption spectra of CCl4 are reported between 200–235
nm as a function of temperature (225–350 K). The results
from this work are critically compared with results from
earlier studies. For N2O, the results are in good agreement
with the current recommended values, enabling a reduction
in the estimated uncertainty in the N2O atmospheric
photolysis rate. For CCl4, the cross section results are
systematically greater than the current recommendation
at the reduced temperatures most relevant to stratospheric
photolysis. The new cross sections result in a 5–7 percent
increase in the modeled CCl4 photolysis loss, and a slight
decrease in the stratospheric lifetime, from 51 to 50 years,
for present-day conditions. The corresponding changes in
modeled inorganic chlorine and ozone in the stratosphere
are quite small. The data from this study will be used as
input for atmospheric models to better define the impact
of these trace gases on stratospheric ozone and climate
change.
Product: Rontu Carlon, N, DK Papanastasiou, EL Fleming,
CH Jackman, PA Newman, and JB Burkholder (2010),
UV absorption cross sections of nitrous oxide (N2O) and
carbon tetrachloride (CCl4) between 210 and 350K and the
atmospheric implications, Atmos. Chem. Phys., 10, 6137–
6149, doi:10.5194/acp-10-6137-2010, 2010.
Milestone 3. Develop and use a new laboratory apparatus
to measure the Henry’s Law solubility of key atmospheric
trace species in aqueous solutions; and measure hydrolysis
rate constants and product yields for reactive species.
Impact: This research will evaluate the partitioning of
trace species between the gas- and aqueous-phase and
the possible significance of aqueous chemistry as an atmospheric
loss process. This research has implications for
both stratospheric ozone and climate-chemistry coupling.
A new experimental methodology for the determination
of Henry’s law constant and hydrolysis rate coefficient of
compounds of atmospheric interest has been developed
and tested thoroughly. The experimental setup is a closedcycle
recirculation temperature–controlled bubble apparatus
connected in series with a Fourier transform infrared
(FTIR) spectrometer to measure the fractional concentration
change of a species in the gas-phase.
Henry’s law solubility constants of many climate-sensitive
atmospheric trace species with low solubility in water,
such as HFC 227ea, NF3, SF6, CH4 and HFC 134a, were
determined as a function of temperature, in pure water
and in buffered solutions of different pH. Hydrolysis rate
coefficients were determined for perfluoro-2-methyl-3-pentatnone
(PFMP), a new fire suppressant with atmospheric
lifetime of approximately 15 days (degraded via UV pho-
CIRES Annual Report 2011 111