Mapping Greenhouse Gas Emissions in the Los Angeles Basin by Remote Sensing Using a

Fourier Transform Spectrometer on Mt. Wilson

Kam Weng (Clare) Wong1, Dejian Fu1, Thomas Pongetti1, Sally Newman2, Eric Kort1, Charles Miller1, Yuk L. Yung2, Stanley Sander1

1Jet Propulsion Laboratory, Pasadena, CA, USA2California Institution of Technology, Pasadena, CA, USA

Copyright 2013. California Institute of Technology. Government sponsorship acknowledged.

Why Cities Matter?

Sources: Duren and Miller, 2012

Photo of nightlight as seen from space showing global distribution of human activities.

Why Cities Matter?

• Cities contributes to the third most GHG emissions in the world, following the United States and China.

• About 50% of world’s population lives in cities (increase to 70% in 2050).

• It is important to track their emissions.

Sources: Duren and Miller, 2012

Source: World Bank, 2010

Photo of nightlight as seen from space showing global distribution of human activities

Why Cities Matter?

Sources: Duren and Miller, 2012

Here, we focus on the Los Angeles basin, one of the biggest megacities in the world.

Source: World Bank, 2010

• Cities contributes to the third most GHG emissions in the world, following the United States and China.

• About 50% of world’s population lives in cities (increase to 70% in 2050).

• It is important to track their emissions.

Sources of CO2 in the LA Basin

Vehicles

Natural gas fueled power plants

• Anthropogenic CO2 emissions in the LA basin primary comes from fossil fuel combustion. Vehicles and power plants are important sources.

• Emissions are understood to within 5-10% (California Air Resources Board, 2008)

Sources of CH4 in the LA Basin

Pipeline leakage

LandfillsWastewater treatment plants

• Methane (CH4) comes from a variety of sources in the LA basin such as wastewater treatment plants, landfills, daily farms and pipeline leakage.

• Emissions in the LA basin have 25-50% uncertainties (Wunch et al., 2009; Hsu et al., 2010; Wennberg et al., 2012).

Dairy farms

How do we estimate emissions?

Top-down Approach -- quantifies emissions based on direct observations of atmospheric concentrations.

• Essential to develop precise emission inventories.• Ratio analysis is a simple way of estimating emission based on observations

of atmospheric concentrations of 2 or more trace gases, when the emission of one of the trace gases is known.

• The current network of continuous CO2 and CH4 measurements is very sparse.

• These observations may be limited to local area which may not represent the entire Los Angeles basin.

Problems and Motivations

Current continuous CO2 and CH4 monitoring stations

100 km

• The current network of continuous CO2 and CH4 measurements is very sparse.

• These observations may be limited to local area which may not represent the entire Los Angeles basin.

Problems and Motivations

Current continuous CO2 and CH4 monitoring stations

There is a need to develop a robust measurement technique which provides continuous temporal and spatial observations in LA basin!

100 km

Direct B

eam

(diffuse reflection fro

m Spectralon plate)

AzimuthalScan Surface Reflection

(Elevation Scan)

FTIR Spectrometer(0.7-2.5 m)

Poin

ting M

irror

16” Cassegrain Telescope (removable)

CO2 at 1.6 m, 2.0 m CH4 at 1.6 m, 2.1 m N2O at 2.3 m CO at 2.3 m O2 at 1.27 m

California Laboratory for Atmospheric Remote Sensing (CLARS)

Long: 118.057°W Lat: 34.221°NAlt: 1.7 km (ASL)

Two modes:1. Direct sun 2. LA Basin Survey

Data filter for clouds/aerosol

High-precision data since Aug 2011

Basin Reflection Points

Standard measurement cycle: FTS points at the 28 reflection points (LA Basin Survey) and makes four direct sun measurements (integration time ~ 2.5 min). There are about 5-8 measurement cycles per day.Special measurement cycle: Specific targets, transects

Direct Sun

West Pasadena

Direct Sun and West Pasadena Observations

In the following slide, we will compare the direct sun and the West Pasadena observations of path-averaged dry air mixing ratios, XCO2 and XCH4.

• Direct sun measurements, which are above the urban dome, show no diurnal variations.• Basin measurements show strong diurnal variations due to basin emissions.

Diurnal Variations of Direct Sun and Basin XCO2 and XCH4

4/18/2012 4/19/2012 9/17/2012 9/18/2012

CO2

CH4

1. Compute the XGAS excess above background resulting from emissions in the basin, by subtracting the direct sun XGAS from the basin XGAS.

2. Correlate the two XGAS excess to investigate the CH4:CO2 emission ratio in the basin.

Understanding the Emissions of CH4 and CO2

Tight correlations between XCO2 and XCH4 excess are observed (for all 28 basin measurements) even though the two GHGs have different sources, due to:

• CO2 and CH4 are emitted with relatively constant ratio, combined with mixing and ventilation processes in the atmosphere.

Correlations Between CH4 and CO2

Spatial Variability of CH4:CO2 Ratio in the LA Basin Atmosphere

• CH4:CO2 ratios show spatial variability, ranging from 5.2 to 7.2• Average CH4:CO2 ratio over all basin measurements is 6.2 +/- 0.23

Increasing distance from Mt. Wilson

OBSERVATIONS CH4:CO2 RATIO

(ppb:ppm)

TYPE OF MEASUREMENT

REFERENCES

TCCON FTS

(Pasadena, 8/2007 – 6/2008)

7.8±0.8 Column Wunch et al. 2009

CLARS FTS

Pasadena, 9/2011 – 10/2012)

7.2±0.2 Column This study

ARCTAS-CARB

(LA basin, 6/2008)

6.8±0. 6 Aircraft in-situ Wennberg et al. 2012

CalNex, LA basin

(LA basin, 5/2010 – 6/2010)

6.6±0. 3 Aircraft in-situ Wennberg et al. 2012

CLARS FTS

(LA basin, 9/2011 – 10/2012)

6.2±0.2 Column This study

Comparison with Previous Studies

Results of this study are In good agreement with previous studies:• In Pasadena

OBSERVATIONS CH4:CO2 RATIO

(ppb:ppm)

TYPE OF MEASUREMENT

REFERENCES

TCCON FTS

(Pasadena, 8/2007 – 6/2008)

7.8±0.8 Column Wunch et al. 2009

CLARS FTS

Pasadena, 9/2011 – 10/2012)

7.2±0.2 Column This study

ARCTAS-CARB

(LA basin, 6/2008)

6.8±0. 6 Aircraft in-situ Wennberg et al. 2012

CalNex, LA basin

(LA basin, 5/2010 – 6/2010)

6.6±0. 3 Aircraft in-situ Wennberg et al. 2012

CLARS FTS

(LA basin, 9/2011 – 10/2012)

6.2±0.2 Column This study

Comparison with Previous Studies

Results of this study are In good agreement with previous studies:• In Pasadena• In the LA basin

• This study demonstrates the ability to measure CO2 and CH4 in the Los Angeles basin using ground based remote sensing technique from Mt. Wilson.

• Observations indicate the current CH4 emission inventory for the Los Angeles basin are underestimated by 20±5%.

• Spatial variability in CH4:CO2 ratio is observed in the Los Angeles basin, indicating the need for ground based remote sensing of CO2 and CH4 from Mt Wilson.

• The long term goal is to assimilate the CO2 and CH4 observations and to improve CO2 and CH4 emission inventories for the Los Angeles basin using atmospheric inversion models.

Conclusions

• This study demonstrates the ability to measure CO2 and CH4 in the Los Angeles basin using ground based remote sensing technique from Mt. Wilson.

• Observations indicate the current CH4 emission inventory for the Los Angeles basin are underestimated by 20±5%.

• Spatial variability in CH4:CO2 ratio is observed in the Los Angeles basin, indicating the need for ground based remote sensing of CO2 and CH4 from Mt Wilson.

• The long term goal is to assimilate the CO2 and CH4 observations and to improve CO2 and CH4 emission inventories for the Los Angeles basin using atmospheric inversion models.

Conclusions

• This study demonstrates the ability to measure CO2 and CH4 in the Los Angeles basin using ground based remote sensing technique from Mt. Wilson.

• Observations indicate the current CH4 emission inventory for the Los Angeles basin are underestimated by 20±5%.

• Spatial variability in CH4:CO2 ratio is observed in the Los Angeles basin, indicating the need for ground based remote sensing of CO2 and CH4 from Mt Wilson.

• The long term goal is to assimilate the CO2 and CH4 observations and to improve CO2 and CH4 emission inventories for the Los Angeles basin using atmospheric inversion models.

Conclusions

• This study demonstrates the ability to measure CO2 and CH4 in the Los Angeles basin using ground based remote sensing technique from Mt. Wilson.

• Observations indicate the current CH4 emission inventory for the Los Angeles basin are underestimated by 20±5%.

• Spatial variability in CH4:CO2 ratio is observed in the Los Angeles basin, indicating the need for ground based remote sensing of CO2 and CH4 from Mt Wilson.

• The long term goal is to assimilate the CO2 and CH4 observations and to improve CO2 and CH4 emission inventories for the Los Angeles basin using atmospheric inversion models.

Conclusions

Thank you!Questions?