© crown copyright met office estimating uk and nw european ch 4 emissions using inversion modelling...

© Crown copyright Met Office

Estimating UK and NW European CH4 emissions using

inversion modelling

Alistair Manning

with thanks to Simon O’Doherty & Dickon Young (University of Bristol)


Overview

• Estimate UK and NWEU (north west European) emissions of greenhouse gases (GHG) totally independent of UNFCCC inventory process.

• Use in-situ high-frequency atmospheric observations from the remote station on the west coast of Ireland (Mace Head).

• Employ an atmospheric dispersion model (NAME) coupled with 3-D meteorology to understand the recent history of the air arriving at Mace Head.

• Two stage process:

• Estimate long-term Northern Hemisphere baseline concentration.

• Estimate regional emissions through inversion modelling (NAME-Inversion).

• Compare NAME-inversion estimates to UNFCCC/EDGAR inventory estimates.


Estimating Baseline Concentrations at remote measurement site (Mace Head)

• NAME model (Lagrangian particle dispersion model) run ‘backwards’.

• Uses 3-D meteorological data from UK Met Office NWP model (25-60 km resolution) and ECMWF ERA Interim (re-analysis) (~80 km).

• Derive air history map for each site for a 2-hour period:

• Combination of tens of thousands of trajectories.

• Darker shade means greater contribution from that area.

• All surface sources within previous 30 days of travel (domain limited) that contribute to an observation during a 2-hour period are recorded.

Mace Head air history maps generated each 2-hour period:• 2003-2011 UK Met Office UM• 1989-2002 ECMWF ERA Interim

Mace Head


Where has the air come from? Examples:

1800-0000 16th March 1996

Baseline

0600-1200 21st March 1996

Polluted

1200-1800 2nd March 1996

Complicated


Baseline Concentration Methodology (1):Classifying Mace Head Observations

Methane: Raw observations (ppb)



Methane (ppb): Observations colour-coded based on recent history of air arriving at the station (Mace Head)



Methane (ppb): Select only those observations that are considered to be from a ‘clean’ non-regionally polluted sector.



Methane (ppb): Baseline observations – Statistically identify outliers (black) and remove



Methane (ppb): Remaining observations classed as ‘baseline’



Methane (ppb): Best-fit (moving window) line through baseline observations



Methane (ppb): Zoom-in on baseline estimate



Methane (ppb): Estimate baseline uncertainty (‘noise’ in baseline)


Mid-latitude baseline concentration of:Methane (ppb)

Baseline

Growth Rate

Seasonal Cycle


Mid-latitude baseline concentration of:Nitrous Oxide (ppb)

Baseline

Growth Rate

Seasonal Cycle


Estimating regional emissions from above baseline concentrations


Estimating Regional Emissions:Inverse Modelling

Aim: Generate emission estimates from ‘polluted’ (above baseline) observations.

Subtract the baseline concentration from each observation.


The NAME-Inversion Method (1)

M [t x m] ¤ e [mx1] = O’ [tx1] = O - b

Dilution matrix

Ba

selin

e

Time series of observations

• Air history maps from Mace Head are generated using NAME model

• Record time-series of relative contributions of each surface source to observation station

Emission map:the

Solution

t2

t3

t1


Dilution matrix = MMeasurement - Baseline = O’ Emission Map = e (the solution)Relationship: M e = O’Problem: Minimise O’ - M e

• Remove observations that have a strong local influence.• Through many iterations find emission distribution that is best-fit statistical

match between model time-series and observations.• No prior information – Random initial guess – Not steered by a priori.• Solve for each 3-yr period stepping monthly e.g. Feb’89 – Jan’92, Mar’89 – Feb’92, …

• Solve multiple times, each time start from different random initial guess.• Apply random ‘baseline noise’ to observations (log-normal distribution).

The NAME-Inversion Method (2)

Air History Map = Matrix M(No times x No grids)


The NAME-Inversion Method (3) :Grid used to Estimate Emissions

• Balance equation so that each grid contributes equally (approximately).

• More distant grids grouped together so have same impact at the observation station. Example: Grouping of grids based on observations

at Mace Head (MH) on west coast of Ireland.

Grids = 25 km, 50 km, 100 km, 200 km, 400 km, 800 km

0.0

10.0

20.0

30.0

40.0

50.0

60.0

0-400 401-800

801-1200

1201-1600

1601-2000

2001-2400

2401-2800

2801-3200

3201-3600

3601-4000

4001-4400

4401-4800

4801-5200

5201-5600

Number of Times Grid Contributes

% o

f G

rid

s t

ha

t C

on

trib

ute

Not Combined

Combined


The NAME-Inversion Method (4) :Resolved areas

UK

NWEU

Mace Head


Model Solutions Vs Observation

‘Best-Fit’ Model (Grey/Black) and Observation (Red) Time-series for methane (ppb) Jan-Mar 2008


Nitrous Oxide

1990

2010


Methane

1990

2010


Conclusions

• Estimate Northern Hemisphere baseline trends 1990-2011 from observation station on west coast of Ireland.

• N2O shows a steady rise, CH4 rising but more irregular.

• NAME-Inversion method used to estimate UK and NW European emissions of N2O and CH4 from 1990 until 2010.

• N2O estimates broadly agree (lower by 10-20% but trend agrees) with UNFCCC inventory.

• CH4 estimates for UK show slow decline (10-20%%) markedly different to UNFCCC trend which shows a 50% reduction over the 20 years but last 5 years agree well.

• CH4 estimate for NW Europe broadly agrees with UNFCCC but with a slightly slower decline.

• Both NAME-Inversion and UNFCCC estimates have significant uncertainties.


Future

• Increasing the number of representative observation sites will increase resolution of the inversion emission estimates

• Improved meteorological models will improve the ability of models to calculate the recent history and dilution of the air

• Satellites – Need to be able to ‘see’ the boundary layer better before they are used more widely

© crown copyright met office estimating uk and nw european ch 4 emissions using inversion modelling...

Documents

mace head air history

baseline uncertainty

remaining observations

observations colour

inversion estimates

recent history of air

inversion method

hour period