) in firn air at Sum m it, Greenland ( 2 0 0 6 ) and W est - - PowerPoint PPT Presentation

Measurem ents of light alkanes ( C2

• C4

) in firn air at Sum m it, Greenland ( 2 0 0 6 ) and W est Antarctic I ce Sheet Divide, Antarctica ( 2 0 0 5 ) : I s there evidence for a recent decline in polar tropospheric levels?

Murat Aydin1, Eric Saltzman1, Margaret B. Williams2, Eric Sofen3, and Mark Battle4

1UC Irvine, Department of Earth System Science 2Bay Area Environmental Research Institute/NASA Ames 3University of Washington, Department of Atmospheric Sciences 4Bowdoin College, Department of Physics and Astronomy

Acknowledgements:

• S. Montzka and J. Butler (NOAA/ESRL-GMD) – UCI flask data

Blake-Rowland Lab. (UCI) – surface flask data

• E. Atlas (U. of Miami) – firn data

Todd Sowers (Penn State) – field NSF/OPP – support ICDS – drilling support

Precursors of O3 and CO and a removal mechanism for OH Summer OH lifetimes: τethane =1-2 months, τpropane =8-20 days, τbutane =2-10 days

NMHC’s – light alkanes (C2 H6 , C3 H8 , n-C4 H10 )

Anthropogenic sources

natural gas and oil leaks Automotive, biomass burning

Natural sources

biomass burning

• ceanic, vegetative, soil emissions (smaller)

Firn air records and modeling

• Smoothed (low-pass filter) records
• Site characteristics impact smoothing
• Exact age calculation impossible
• All ages (CO2

, CFC-12, mean) represent an integrated average

• Summit and WAIS-D firn modeling with

diffusivity tuning using CO2 and CFC-12.

Summit surface measurements 1997-2007 and seasonality in Summit firn (Blake-Rowland and UCI)

• No clear long-term trend
• Mean levels
• ethane: 1250-1500 ppt
• propane: 400-600 ppt
• n-butane: 150-250 ppt
• Annual mean signal observed in firn below 40 m

1/1/1997 1/1/1999 1/1/2001 1/1/2003 1/1/2005 1/1/2007 1000 2000 3000 400 800 1200 150 300 450

Date ethane (ppt) propane (ppt) n-butane (ppt)

Summit UCI firn data (ethane, propane, n-butane)

1200 1350 1500 1650 1800 1950 2100 80 60 40 20 80 60 40 20 100 200 300 400 500 600 80 60 40 20 100 200 300 400 500 600

depth in firn (m) ethane (ppt)

Seasonality

propane - butane (ppt)

66 m 76 m

1900 1920 1940 1960 1980 2000 1000 1200 1400 1600 1800 2000 2200

Summit ethane data Atmospheric history

ethane (ppt) date

~10% damping of peak 1200 1350 1500 1650 1800 1950 2100 80 60 40 20

depth in firn (m) ethane (ppt)

Incorporation of atmospheric signal into firn Change in alkanes 1970-1990 C2H6 C3H8 n-C4H10 Rate 29 ppt/y 9 ppt/y 4 ppt/y Overall 27% 27% 28%

Summit (UCI) and NGRIP (E. Atlas), Greenland data (depths > 40 m)

Similar trends at both sites: 1970s peak, decrease during 1980s and on Apparent disagreement C2 H6 : bottom of the firn C3 H8 : shallow firn n-C4 H10 : shallow firn

1950 1960 1970 1980 1990 2000 1350 1500 1650 1800 1950 2100 UCI - Summit

• E. Atlas - NGRIP

ethane (ppt) date from mean age

1950 1960 1970 1980 1990 2000 400 500 600 700 UCI - Summit

• E. Atlas - NGRIP

propane (ppt) date from mean age

1950 1960 1970 1980 1990 2000 120 160 200 240 280 UCI - Summit

• E. Atlas - NGRIP

n-butane (ppt) date from mean age

SH surface measurements 2000-2007 and seasonality in WAIS-D firn (Blake- Rowland and UCI)

• No spatial variability, no clear long-term trend
• Mean levels
• C2

H6 : ~200 ppt

• C3

H8 : ~25 ppt

• n-C4

H10 : ~8 ppt

• Annual mean below 40 m at WAIS-D (similar to Summit)

2000.0 2000.2 2000.4 2000.6 2000.8 2001.0 50 100 150 200 250 300 350 400

climatology fit to climatology

ethane (ppt) time of year

140 160 180 200 220 80 60 40 20

WAIS-D firn depth (m) ethane (ppt)

1/1/2000 1/1/2002 1/1/2004 1/1/2006 1/1/2008 100 200 300 400 20 40 60 5 10 15 20 SPO - Blake&Rowland South Pole Cape Grim Palmer

Date ethane (ppt) propane (ppt) n-butane (ppt)

100 120 140 160 180 200 220 240 260 280 80 70 60 50 40 30 20 10 80 70 60 50 40 30 20 10 10 20 30 40 50 60 70 80 70 60 50 40 30 20 10

WAIS-D firn depth (m) ethane (ppt) propane and butane (ppt) Seasonality

WAIS-D UCI firn data (C2 H6 , C3 H8 , n-C4 H10 )

WAIS-D ethane

• stabilization in 1980s
• drop in 1990s (~30%)

WAIS-D propane and n-butane

• More noise
• May be a similar drop in propane

1900 1920 1940 1960 1980 2000 80 120 160 200 240 280

ethane (ppt) date

Incorporation of atmospheric signal into firn

WAIS-D (UCI) and South Pole (E. Atlas) data (depths > 40 m)

• WAIS-D and SPO agree, trends from DML don’t (more/better data from

Antarctica

• SPO and WAIS-D data together suggest a ~30% decline in ethane
• Roughly synchronous with changes at Summit, Greenland
• Fidelity of firn record still a question

1940 1950 1960 1970 1980 1990 2000 120 160 200 240 280 320

• E. Atlas, SPO

UCI, WAIS-D Kaspers et al. (2004), DML

ethane (ppt) CO2 - CFC-12 age

1940 1950 1960 1970 1980 1990 2000 5 10 15 20 25 30 35 40 45 50

• E. Atlas - SPO

UCI - WAIS-D Kaspers et al. (2004), DML

propane (ppt) CO2 - CFC-12 age

WHY are NMHC’s decreasing at polar latitudes? (possibly globally!) Sources: Fossil fuel consumption Sink: OH, Cl

Sources: Hydrocarbon fuel use efficiency must have improved dramatically?

World Dry Natural Gas Consumption

10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 P2006 billion cubic feet Asia&Oceania Africa Mideast Europe Cnt&Sth America

• N. America
• Consumption/production going

up

• Short lifetimes imply source

loading must be continually dropping

• Both hemispheres (may be)

Source: Energy Information Administration, Office of Energy Markets and End Use

Can we trust the fidelity of the firn record?

Surface air analysis:

• Ongoing at UCI with NOAA flasks

Firn air data – firn modeling:

• back to Summit in 2008
• new SPO firn sampling in 08-09

1/6/1950 1/6/1960 1/6/1970 1/6/1980 1/6/1990 1/6/2000 1/6/2010 500 1000 1500 2000 2500 3000

Rowland-Blake UCI-NOAA Firn 2006

Date Summit ethane (ppt)

Ice Cores