Urban CO2 Emissions from the Los Angeles Basin: Assessing chemistry and dynamics using the suite of tracers measured aboard the CalNex WP-3 Aircraft

Steven C. Wofsy, Gregory Santoni, Bin Xiang, Bruce C. Daube, Jasna Pittman, Eric Kort, Kathryn McKain, Roísin Commane, Elaine Gottlieb Harvard University Presented at the CalNEX Science Team Meeting, Scramento, CA 16 May 2011

Goals for studying CO2 and other GHGs in

CalNEX

• Use of CO2 as the primary metric of

combustion influence

• Test ideas of how to measure changes in

total emissions over time (treaty verification)

• Use CO2 as a model validation tool

Mt. Wilson

Background CO2, CO, CH4 concentrations: Mt. Wilson vs from the P-3

DOY 2010

ΔCO/ΔCO2 = 11±2 TCCON –Wunch et al. (2009)

ΔC

O (

ppb)

ΔCO2 (ppm)

Uniformity an artifact of an aged mix of sources?

Mean Vertical Distributions of

ΔCO2 on 10 flight days over

Los Angeles

ΔCH4/ΔCO2 = 8 ± 0.8 TCCON

P-3

ΔN2O/ΔCO2 = .5 ± .3 TCCON

stratosphere?

15 17 19 21

UTC Hr

X

-CO

2 (

full

atm

osphere

) [

TC

CO

N]

38

5

3

87 389

391

P-3 Δ-XCO2 0-3.5 km

Δ-X

CO

2 (

ppm

)

0

2

4

6

DOY 2010

1200

local

Locations of urban measurement sites in the Salt Lake Valley. Photos show placement & locale.

Salt Lake City: A contrast site vs. Los Angeles

Variation of background air entering the SLC Valley

150 200 250 300 350 Day of Year (2006)

CO

2 (

pp

m)

3

75

38

0

3

85

39

0

Data from Britt Stephens

— Snowbird

✚ Wendover

SLC CO2 (Vulcan emissions in μmole/m2/s)

SLC CO2 (Vulcan emissions in tonne C/hr)

11 13 15 17 19 21 23 25

Date (October, 2006)

CO

2 (

ppm

)

40

0 4

50

5

00

5

50

6

00

Observed and Modeled CO2 concentrations, Salt Lake City (Downtown)

— Observed

— Model, 4 km

— Model 1.3 km + UCM

Hour, Local Time

Obs. vs model CO2 at 3 sites in Salt Lake City, Oct.

2006, from hi-resolution model (1.3 km, urban

canopy). Hourly points in gray and 8-hour averages in

red. Line is SMA fit to 8-hour data.

Obs. CO2

Modele

d C

O2 1:1

Inventory correction factors for Salt Lake City

How could the inventory be so far off ??

The effect of inhomogeneous spatial

distribution of emissions on aggregated

source models.

Heig

ht

agl (m

)

0

2500

40 40.8

deg Lat

40 40.8

deg Lat

40 40.8 40 40.8 40 40.8 40 40.8

40

4

1

-112.5 -111.5

Summary of results

•CO2 is an excellent tracer of combustion influence

in Los Angeles, with overwhelming dominance of

fossil fuels and an aged mix of basin-wide sources.

•Methane emission rates are large.

•Total column measurements are most likely to

provide independent verification of emission rates.

•Detailed modeling of CO2 or other long-lived

emissions in urban areas requires a priori

knowledge of source spatial and temporal

distributions, not usually available. Less important

in Los Angeles than in most other cities.

Obs. vs model CO2 at 3 sites in Salt Lake City, Oct. 2006. Top

row: model and obs. from hi-resolution model (1.3 km, urban

canopy). Bottom: 4 km baseline model. Hourly points in gray

and 8-hour averages in red. Lines are SMA fits to 8-hour data.