S. Solomon, D.J. Ivy, D. Kinnison, M.J. Mills, R.R. Neely III, and A. Schmidt, Emergence of healing in the Antarctic ozone layer.
Science, 2016, accepted |
Industrial chlorofluorocarbons that cause ozone depletion have been phased out under the Montreal
Protocol. A chemically-driven increase in polar ozone (or “healing”) is expected in response to
this historic agreement. Observations and model calculations taken together indicate that the
onset of healing of Antarctic ozone loss has now emerged in September. Fingerprints of September
healing since 2000 are identified through (i) increases in ozone column amounts, (ii) changes in
the vertical profile of ozone concentration, and (iii) decreases in the areal extent of the
ozone hole. Along with chemistry, dynamical and temperature changes contribute to the healing,
but could represent feedbacks to chemistry. Volcanic eruptions episodically interfere with healing,
particularly during 2015 (when a record October ozone hole occurred following the Calbuco eruption).
P.G. Simmonds, et al., Global and regional emissions estimates of 1, 1-difluoroethane (HFC-152a, CH3CHF2)
from in situ and air archive observations. Atmos. Chem. Phys., 2015, accepted
D.J. Ivy, S. Solomon, and H.E. Rieder, Radiative and Dynamical Influences on Polar Stratospheric Temperature Trends.
J. Climate, 2015, accepted
S. O'Doherty, et al., Global emissions of HFC-143a (CH3CF3) and HFC-32 (CH2F2)
from in situ and air archive atmospheric observations.
Atmos. Chem. and Phys., 2014, 14:9249-9258 |
High-frequency, in situ observations from the Advanced Global Atmospheric Gases Experiment (AGAGE), for the period 2003 to 2012, combined with
archive flask measurements dating back to 1977, have been used to capture the rapid growth of HFC-143a (CH3CF3) and HFC-32 (CH2F2) mole fractions
and emissions into the atmosphere. Here we report the first in situ global measurements of these two gases. HFC-143a and HFC-32 are the third
and sixth most abundant hydrofluorocarbons (HFCs) respectively and they currently make an appreciable contribution to the HFCs in terms of
atmospheric radiative forcing (1.7 ± 0.04 and 0.7 ± 0.02 mW m−2 in 2012 respectively). In 2012 the global average mole fraction of HFC-143a
was 13.4 ± 0.3 ppt (1σ) in the lower troposphere and its growth rate was 1.4 ± 0.04 ppt yr−1; HFC-32 had a global mean mole fraction of 6.2 ± 0.2
ppt and a growth rate of 1.1 ± 0.04 ppt yr−1 in 2012. The extensive observations presented in this work have been combined with an atmospheric
transport model to simulate global atmospheric abundances and derive global emission estimates. It is estimated that 23 ± 3 Gg yr−1 of HFC-143a
and 21 ± 11 Gg yr−1 of HFC-32 were emitted globally in 2012, and the emission rates are estimated to be increasing by 7 ± 5% yr−1 for HFC-143a
and 14 ± 11% yr−1 for HFC-32.
S. Solomon, J. Haskins, D.J. Ivy, and F. Min, Fundamental Differences Between Arctic and Antarctic Ozone Depletion.
PNAS, 2014, 111, 6220-6225 |
Fundamental differences in observed ozone depletion between the Arctic and the Antarctic are shown,
clarifying distinctions between both average and extreme ozone decreases in the two hemispheres. Balloon-borne and satellite measurements
in the heart of the ozone layer near 18−24 km altitude show that extreme ozone decreases often observed in the Antarctic ozone hole region
have not yet been measured in the Arctic in any year, including the unusually cold Arctic spring of 2011. The data provide direct evidence
that heavily depleted air contains reduced nitric acid abundances, and better quantify the roles of polar stratospheric cloud chemistry and
temperatures below −80°C to −85°C in ozone destruction.
T. Arnold, et al., HFC-43-10mee atmospheric abundances and global emission estimates.
GRL, 2014, 41, 2228-2235 |
We report in situ atmospheric measurements of hydrofluorocarbon HFC-43-10mee (C5H2F10; 1,1,1,2,2,3,4,5,5,5-decafluoropentane) from seven
observatories at various latitudes, together with measurements of archived air samples and recent Antarctic flask air samples. The global
mean tropospheric abundance was 0.21 ± 0.05 ppt (parts per trillion, dry air mole fraction) in 2012, rising from 0.04 ± 0.03 ppt in 2000.
We combine the measurements with a model and an inverse method to estimate rising global emissions-from 0.43 ± 0.34 Gg yr−1 in 2000 to
1.13 ± 0.31 Gg yr−1 in 2012 (~1.9 Tg CO2-eq yr−1 based on a 100 year global warming potential of 1660). HFC-43-10mee—a cleaning solvent
used in the electronics industry—is currently a minor contributor to global radiative forcing relative to total HFCs; however, our calculated
emissions highlight a significant difference from the available reported figures and projected estimates.
M. Rigby, et al., Recent and future trends in synthetic greenhouse gas radiative forcing.
GRL, 2014, 41, 2623-2630 |
Atmospheric measurements show that emissions of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons are now the primary drivers of
the positive growth in synthetic greenhouse gas (SGHG) radiative forcing. We infer recent SGHG emissions and examine the impact of
future emissions scenarios, with a particular focus on proposals to reduce HFC use under the Montreal Protocol. If these proposals are
implemented, overall SGHG radiative forcing could peak at around 355 mW m−2 in 2020, before declining by approximately 26% by 2050,
despite continued growth of fully fluorinated greenhouse gas emissions. Compared to “no HFC policy” projections, this amounts to a reduction
in radiative forcing of between 50 and 240 mW m−2 by 2050 or a cumulative emissions saving equivalent to 0.5 to 2.8 years of CO2 emissions
at current levels. However, more complete reporting of global HFC emissions is required, as less than half of global emissions are currently
D.J. Ivy, S. Solomon, and D.W.J. Thompson, On the Identification of the Downward Propagation of Arctic Stratospheric Climate Change over Recent Decades.
J. Climate, 2014, 27, 2789-2799 |
Dynamical coupling between the stratospheric and tropospheric circumpolar circulations in the Arctic has been widely documented on
month-to-month and interannual time scales, but not on longer time scales. In the Antarctic, both short- and long-term coupling
extending from the stratosphere to the surface has been identified. In this study, changes in Arctic temperature, geopotential height,
and ozone observed since the satellite era began in 1979 are examined, comparing dynamically quiescent years in which major sudden
stratospheric warmings did not occur to all years. It is shown that this approach clarifies the behavior for years without major warmings
and that dynamically quiescent years are marked by a strengthening of the Arctic polar vortex over the past 30 years. The associated
declines in stratospheric temperatures, geopotential height, and ozone are qualitatively similar to those obtained in the Antarctic
(albeit weaker), and propagate downward into the Arctic lowermost stratosphere during late winter and early spring. In sharp contrast
to the Antarctic, the strengthening of the Arctic stratospheric vortex appears to originate at a higher altitude, and the propagation
to the Arctic troposphere is both very limited and confined to the uppermost troposphere, even when only dynamically quiescent years
are considered in the analysis.
T. Arnold, et al., Nitrogen trifluoride global emissions estimated from updated atmospheric measurements.
PNAS, 2013, 110(6), 2029-2034 |
Nitrogen trifluoride (NF3) has potential to make a growing contribution to the Earth’s radiative budget; however, our understanding of its
atmospheric burden and emission rates has been limited. Based on a revision of our previous calibration and using an expanded set of
atmospheric measurements together with an atmospheric model and inverse method, we estimate that the global emissions of NF3 in 2011 were
1.18 ± 0.21 Gg⋅y−1, or ∼20 Tg CO2-eq⋅y−1 (carbon dioxide equivalent emissions based on a 100-y global warming potential of 16,600 for NF3).
The 2011 global mean tropospheric dry air mole fraction was 0.86 ± 0.04 parts per trillion, resulting from an average emissions growth rate of
0.09 Gg⋅y−2 over the prior decade. In terms of CO2 equivalents, current NF3 emissions represent between 17% and 36% of the emissions of other
long-lived fluorinated compounds from electronics manufacture. We also estimate that the emissions benefit of using NF3 over hexafluoroethane
(C2F6) in electronics manufacture is significant—emissions of between 53 and 220 Tg CO2-eq⋅y−1 were avoided during 2011. Despite these savings,
total NF3 emissions, currently ∼10% of production, are still significantly larger than expected assuming global implementation of ideal
industrial practices. As such, there is a continuing need for improvements in NF3 emissions reduction strategies to keep pace with its
increasing use and to slow its rising contribution to anthropogenic climate forcing.
D.J. Ivy, et al., Global emission estimates and radiative impact of C4F10, C5F12, C6F14, C7F16 and C8F18.
Atmos. Chem. and Phys., 2012, 12: 7635-7645 |
Global emission estimates based on new atmospheric observations are presented for the acylic high molecular weight perfluorocarbons (PFCs):
decafluorobutane (C4F10), dodecafluoropentane (C5F12), tetradecafluorohexane (C6F14), hexadecafluoroheptane (C7F16) and octadecafluorooctane
(C8F18). Emissions are estimated using a 3-dimensional chemical transport model and an inverse method that includes a growth constraint on
emissions. The observations used in the inversion are based on newly measured archived air samples that cover a 39-yr period, from 1973 to 2011,
and include 36 Northern Hemispheric and 46 Southern Hemispheric samples. The derived emission estimates show that global emission rates were
largest in the 1980s and 1990s for C4F10 and C5F12, and in the 1990s for C6F14, C7F16 and C8F18. After a subsequent decline, emissions have
remained relatively stable, within 20%, for the last 5 yr. Bottom-up emission estimates are available from the Emission Database for Global
Atmospheric Research version 4.2 (EDGARv4.2) for C4F10, C5F12, C6F14 and C7F16, and inventories of C4F10, C5F12 and C6F14 are reported to the
United Nations' Framework Convention on Climate Change (UNFCCC) by Annex 1 countries that have ratified the Kyoto Protocol. The atmospheric
measurement-based emission estimates are 20 times larger than EDGARv4.2 for C4F10 and over three orders of magnitude larger for C5F12 (with
2008 EDGARv4.2 estimates for C5F12 at 9.6 kg yr−1, as compared to 67±53 t yr−1 as derived in this study). The derived emission estimates for
C6F14 largely agree with the bottom-up estimates from EDGARv4.2. Moreover, the C7F16 emission estimates are comparable to those of EDGARv4.2
at their peak in the 1990s, albeit significant underestimation for the other time periods. There are no bottom-up emission estimates for C8F18,
thus the emission rates reported here are the first for C8F18. The reported inventories for C4F10, C5F12 and C6F14 to UNFCCC are five to ten times
lower than those estimated in this study.
D.J. Ivy, et al., Atmospheric histories and growth trends of C4F10, C5F12, C6F14, C7F16 and C8F18.
Atmos. Chem. and Phys., 2012, 12: 4313-4325 |
Atmospheric observations and trends are presented for the high molecular weight perfluorocarbons (PFCs): decafluorobutane (C4F10),
dodecafluoropentane (C5F12), tetradecafluorohexane (C6F14), hexadecafluoroheptane (C7F16) and octadecafluorooctane (C8F18). Their atmospheric
histories are based on measurements of 36 Northern Hemisphere and 46 Southern Hemisphere archived air samples collected between 1973 to 2011
using the Advanced Global Atmospheric Gases Experiment (AGAGE) "Medusa" preconcentration gas chromatography-mass spectrometry systems. A new
calibration scale was prepared for each PFC, with estimated accuracies of 6.8% for C4F10, 7.8% for C5F12, 4.0% for C6F14, 6.6% for C7F16 and
7.9% for C8F18. Based on our observations the 2011 globally averaged dry air mole fractions of these heavy PFCs are: 0.17 parts-per-trillion
(ppt, i.e., parts per 1012) for C4F10, 0.12 ppt for C5F12, 0.27 ppt for C6F14, 0.12 ppt for C7F16 and 0.09 ppt for C8F18. These atmospheric
mole fractions combine to contribute to a global average radiative forcing of 0.35 mW m−2, which is 6% of the total anthropogenic PFC radiative
forcing (Montzka and Reimann, 2011; Oram et al., 2012). The growth rates of the heavy perfluorocarbons were largest in the late 1990s peaking
at 6.2 parts per quadrillion (ppq, i.e., parts per 1015) per year (yr) for C4F10, at 5.0 ppq yr-1 for C5F12 and 16.6 ppq yr-1 for C6F14 and in
the early 1990s for C7F16 at 4.7 ppq yr-1 and in the mid 1990s for C8F18 at 4.8 ppq yr-1. The 2011 globally averaged mean atmospheric growth
rates of these PFCs are subsequently lower at 2.2 ppq yr-1 for C4F10, 1.4 ppq yr-1 for C5F12, 5.0 ppq yr−1 for C6F14, 3.4 ppq yr-1 for C7F16
and 0.9 ppq yr-1 for C8F18. The more recent slowdown in the growth rates suggests that emissions are declining as compared to the 1980s and
T. Arnold, J. Mühle, P.K. Salameh, C.M. Harth, D.J. Ivy, and R.F. Weiss, Automated high-frequency measurement of nitrogen trifluoride in ambient air.
Anal. Chem., 2012, 84, 4798-4804 |
We present an analytical method for the in situ measurement of atmospheric nitrogen trifluoride (NF3), an anthropogenic gas with a 100-year
global warming potential of over 16,000. This potent greenhouse gas has a rising atmospheric abundance due to its emission from a growing
number of manufacturing processes and an expanding end-use market. Here we present a modified version of the “Medusa” preconcentration gas
chromatography/mass spectrometry (GC/MS) system of Miller et al. (2008). By altering the techniques of gas separation and chromatography after initial preconcentration,
we are now able to make atmospheric measurements of NF3 with relative precision <2% (1σ) for current background clean air samples. Importantly,
this method augments the currently operational Medusa system, so that the quality of data for species already being measured is not compromised and
NF3 is measured from the same preconcentrated sample. We present the first in situ measurements of NF3 from La Jolla, California made 11 times daily,
illustrating how global deployment of this technique within the AGAGE (Advanced Global Atmospheric Gases Experiment) network could facilitate estimation
of global and regional NF3 emissions over the coming years.
M. K. Vollmer, et al., Atmospheric histories and global emissions of anthropogenic hydrofluorcarbons HFC-365mfc, HFC-245fa, HFC-227ea, and HFC-236fa.
J. Geophys. Res., 2011, 116: D08304 |
We report on ground-based atmospheric measurements and emission estimates of the four anthropogenic hydrofluorocarbons (HFCs) HFC-365mfc
(CH3CF2CH2CF3, 1,1,1,3,3-pentafluorobutane), HFC-245fa (CHF2CH2CF3, 1,1,1,3,3-pentafluoropropane), HFC-227ea (CF3CHFCF3, 1,1,1,2,3,3,3-heptafluoropropane),
and HFC-236fa (CF3CH2CF3, 1,1,1,3,3,3-hexafluoropropane). In situ measurements are from the global monitoring sites of the Advanced Global Atmospheric Gases
Experiment (AGAGE), the System for Observations of Halogenated Greenhouse Gases in Europe (SOGE), and Gosan (South Korea). We include the first halocarbon
flask sample measurements from the Antarctic research stations King Sejong and Troll. We also present measurements of archived air samples from both hemispheres
back to the 1970s. We use a two-dimensional atmospheric transport model to simulate global atmospheric abundances and to estimate global emissions. HFC-365mfc
and HFC-245fa first appeared in the atmosphere only ∼1 decade ago; they have grown rapidly to globally averaged dry air mole fractions of 0.53 ppt (in parts per
trillion, 10−12) and 1.1 ppt, respectively, by the end of 2010. In contrast, HFC-227ea first appeared in the global atmosphere in the 1980s and has since grown
to ∼0.58 ppt. We report the first measurements of HFC-236fa in the atmosphere. This long-lived compound was present in the atmosphere at only 0.074 ppt in 2010.
All four substances exhibit yearly growth rates of >8% yr-1 at the end of 2010. We find rapidly increasing emissions for the foam-blowing compounds HFC-365mfc and
HFC-245fa starting in ∼2002. After peaking in 2006 (HFC-365mfc: 3.2 kt yr-1, HFC-245fa: 6.5 kt yr-1), emissions began to decline. Our results for these two
compounds suggest that recent estimates from long-term projections (to the late 21st century) have strongly overestimated emissions for the early years of the
projections (∼2005–2010). Global HFC-227ea and HFC-236fa emissions have grown to average values of 2.4 kt yr-1 and 0.18 kt yr-1 over the 2008–2010 period,
D. Ivy, J.A. Mulholland and A.G. Russell, Development of Ambient Air Quality Population Metrics for Use in Time-Series Health Studies.
JAWMA, 2008, 58: 711-720 |
A robust methodology was developed to compute population-weighted daily measures of ambient air pollution for use in time-series studies of acute health effects.
Ambient data, including criteria pollutants and four fine particulate matter (PM) components, from monitors located in the 20-county metropolitan Atlanta area over
the time period of 1999–2004 were normalized, spatially resolved using inverse distance-square weighting to Census tracts, denormalized using descriptive spatial models,
and population-weighted. Error associated with applying this procedure with fewer than the maximum number of observations was also calculated. In addition to providing
more representative measures of ambient air pollution for the health study population than provided by a central monitor alone and dampening effects of measurement error
and local source impacts, results were used to evaluate spatial variability and to identify air pollutants for which ambient concentrations are poorly characterized.
The decrease in correlation of daily monitor observations with daily population-weighted average values with increasing distance of the monitor from the urban center was
much greater for primary pollutants than for secondary pollutants. Of the criteria pollutant gases, sulfur dioxide observations were least representative because of the
failure of ambient networks to capture the spatial variability of this pollutant for which concentrations are dominated by point source impacts. Daily fluctuations in PM of
particles less than 10 µm in aerodynamic diameter (PM10) mass were less well characterized than PM of particles less than 2.5 µm in aerodynamic diameter (PM2.5) mass because
of a smaller number of PM10 monitors with daily observations. Of the PM2.5 components, the carbon fractions were less well spatially characterized than sulfate and nitrate
both because of primary emissions of elemental and organic carbon and because of differences in measurement techniques used to assess these carbon fractions.
D.J. Ivy et al., Observed Changes in the Southern Hemispheric Circulation in May, submitted to J. Climate.