Monitoring and Modelling of PM2.5

Aaron van Donkelaar and Randall MartinOctober 4, 2012

Introduction

Three sources of information:• Measured• Chemical Transport Models• Remote Sensing

Three important questions:• How accurate is it?• How spatially

representative is it?• How temporal

representative is it?

• Most direct and accurate data source

• Essential for validation

Network dependent• Data accessibility• Site density• Collection

method/standard• Site selection criteria

Measured observations are essential

The SPARTAN network is developing to increase global in-situ coverage

• Location Criteria– High population density– Proximity to AERONET (AOD)

observations– Uncertainty in PM2.5

concentrations

• Strong Potential– Publically available– Globally consistent– Highly relevant for satellite-

derived PM2.5

Chemical Transport Models (CTM) allow continuous, global coverage

• Detailed aerosol-oxidant chemistry• Resolution of 100’s x 100’s km• Numerous tracers, 100’s reactions• Assimilated meteorology

• Year-specific emissions• Dust, sea salt, sulfate-ammonium-nitrate

system, organic carbon, black carbon, SOA

CTM accuracy varies by region

• Accuracy due to impact of:– Local emission inventories– Regionally relevant chemical reactions– Meteorology

• Able to test impact of emissions using case studies

Outside NA:r = 0.63 (0.71)slope = 0.51 (0.56)bias = 8.51 (2.75) μg/m3

Within NA:r =0.87slope = 1.26bias = -3.14 μg/m3

GEOS-Chem v8-01-04

Satellite retrievals give total aerosol column

Beijing

Aug 13, 2008PM10 = 12 μg m-3

Aug 18, 2008PM10 = 278 μg m-3BBC

Satellite retrievals rely on the same principles as surface visibility…

Loss of contrast

Increased reflectance

…but look through the entire atmosphere down to the surface

Gangetic River Valley, India

We relate satellite-based retrievals of aerosol optical depth (τ) to PM2.5 using a global chemical transport model

The aerosol column is related to PM2.5

Estimated PM2.5 = η· τ

GEOS-ChemChemical Transport Model

vertical structure ▪aerosol type ▪

meteorological effects ▪

8

MISR- Multi-angle- 4 bands- 6-9 day

coverage

MODIS- Single

viewpoint- 36 bands- daily coverage

van Donkelaar et al.Environ. Health Perspect. 2010

Atmos Environ. 2011

Significant agreement with coincident ground measurements over NA

SatelliteDerived

In-situ

Sat

ellit

e-D

eriv

ed [

μg/

m3]

In-situ PM2.5 [μg/m3]

Ann

ual M

ean

PM

2.5 [

μg/

m3]

(200

1-20

06)

r

MODIS τ 0.40

MISR τ 0.54

Combined τ 0.63

Combined PM2.5 0.77

9

• Accuracy impacted by– Representation of surface brightness– Simulated aerosol vertical profile

• Sampling affected by cloud cover and snow

Satellite-derived PM2.5 shows global agreement

Outside Canada/USN = 244 (84 non-EU)r = 0.83 (0.83)Slope = 0.86 (0.91)Bias = 1.15 (-2.64) μg/m3

CTM Agreement:r = 0.63 (0.71)slope = 0.51 (0.56)bias = 8.51 (2.75) μg/m3

A Combined PM2.5/NO2 Indicator from Satellite

𝑀𝑃𝐼=𝑃𝑀 2.5

𝐴𝑄𝐺𝑃𝑀 2.5[1+ 𝑁𝑂2

𝐴𝑄𝐺𝑁𝑂 2]

Cooper et al., EHP, 2012

PM2.5

NO2

0 1 2 5 7 9 11 13 15Satellite-Based Multipollutant Index (Unitless)

MPI0 4 8 12

ShanghaiBeijing

DelhiKarachi

SeoulCairoLima

TehranLos Angeles

BerlinMoscowNairobi

PM2.5 [μg/m

3]M

PI [unitless]

East

ern

Chin

a

150

75

015

7.5

0

PM2.5 [μg/m

3]M

PI [unitless]

Mos

cow

25

15

5

2.5

1.5

0.5

*Satellite-based surface NO2 concentrations can be estimated using a CTM to relate the column to surface quantities similar to satellite-derived PM2.5.

Remote sensed, modelled and measured PM2.5 each improve global monitoring

Future Work

Remote Sensing:Improved algorithms to increase accuracy and resolution

Modelling:Develop representation of processesDevelop assimilation capability to inform AOD/PM2.5

Measurements:More needed for evaluation throughout the world

AcknowledgementsHealth Canada

NSERCNASA