Aerosol Formation in the Atmosphere

David CockerDepartment of Chemical and Environmental Engineering

CE-CERT

Program Goal• Development of a detailed chemical mechanism

for the prediction of ozone, toxics, and secondary organic aerosol(SOA) formation within the atmosphere

– Studies of ozone and SOA at VOC and NOx levels similar to the urban atmosphere

– Investigation of gas-particle partitioning of semi-volatile compounds in the presence of ambient particle loadings

– Improved interpretation of ambient data obtained using aerosol mass spectrometers

Ozone• Created by a chemical reaction between volatile

organic compounds (VOCs) and oxides of nitrogen (NOx) in the presence of sunlight.

VOC + NOx + sunlight Ozone• Lung irritant• Permanent lung damage• Asthmatic trigger asthma• Reduced lung function• Increased respiratory illnesses. • Plant and ecosystem damage.

U.S. Counties in non-attainment for Phase II Ozone Rule, 2005

(0.08 ppm for 8 hr standard)

www.epa.gov

Fine Particulate Matter• Microscopic liquids and/or solids sufficiently small to

deeply penetrate the lungs. • Study Motivated by Clean Air Rules, 2004

– Health-based Standards• Linked to premature death • Aggravation of cardiovascular and respiratory disease• Decreased lung function• Asthmatic triggers• Coughing/wheezing/difficulty breathing

• Many counties in most populous regions within the United States designated as non-attainment areas

U.S. Counties in non-attainment for fine particle standard, 2005

(65 µg m-3 for 8 hr standard)

www.epa.gov

Fine Particulate Matter

• Secondary aerosol can contribute to the majority of fine particulate mass concentrations in polluted regions

• SOA significant contributor to fine particle concentrations in urban airsheds– Up to 80% of urban organic carbon attributed to

secondary organic aerosol

Sources of PM2.5 in Western Riverside County

R2 = 0.91χ2 = 0.53% MB = 115.9

Aerosol Round The World

Q. Zhang, et al.GRL, 34:L13801, 2007

Fine particulate matter• Visibility reduction:

Pasadena, CA

Fine particulate matter• Global radiative forcing (direct and indirect)

thereby affect global climate change

Health Effect

Climate Effect

Regional Air Quality

How does Aerosol Affect us?

“Exposures to air pollution can shorten life by about 14 years for people who die prematurely”

— CARB 2007

Impacts of PM 2.5 Pollutionin South Coast Basin

Source: California Air Resources Board, 2007; 1999-2000 Air Quality Data

Air Quality Modeling OverviewScenario

Conditions Emissions Control Strategies

Air Quality Model

Air Quality Predictions

Health and Social Impacts

Other Model Components

Chemical Mechanism

Critical to predicting secondary pollutants

Source Characterization

International Shipping Trade Routes -infranetlab.org/blog/2008/10/goodbye-global/

Ports of Los Angeles and Long Beach• Nation’s largest container cargo port complex•>40 % of nation’s containerized imports arrive here

Various Port Sources

Engines on OGVs• Main Propulsion Engine

– Two Stroke– Displacement > 1000 liters/Cyl

(6-12 cyl)– 54,000 kW, 90 rpm

• Auxiliary Engine– Four Stroke– Displacement > 10 liters/Cyl

(6cyl)– 900 kW, 900 rpm

Main Engine Cylinder

21

Test Fuels• Heavy Fuel Oil (HFO)

– Commonly known as bunker fuel or residual oil– Residual fraction from crude refining– Used on main engine and boiler– Very high viscosity and high sulfur content (2.6% m/m)

• Marine Gas Oil and Marine Distillate Oil– Refined fraction from crude distillation– Used on auxiliary engine– Lower sulfur content (0.16 %m/m)

Sulfuric Acid – Stack Damage

23

Photograph taken of the container ship from the cabin of the CIRPAS Twin

Otter

Particle Size• Soot (Dprimary~30nm)• Nanoparticles(5-8nm)• Unknown particles( 30-80nm)

• EDS found V and S both from nanoparticles and unknown particles.

Comparison of PM Emissions (g/kg CO2)

3

2.5

1

0.75

0.5

0.25

0

HDD trucks SwitchingLocomotives

Ship MainEngine

Ship AuxiliaryEngine

Yard Tractor BUG Aircraft

g/kg

CO

2

Total Hydrocarbon Emissions (g/kg CO2)

0

0.25

0.5

0.75

1

1.25

3

HDD trucks SwitchingLocomotives

Ship MainEngine

Ship AuxiliaryEngine

Yard Tractor BUG Aircraft

g/kg

CO

2

`

Comparison of PM Emissions (g/mile/ton)

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

1994-97 1998 1999-2002

SD-18 SD-20 SW-1200St1

SW-1200St2

MainEngine

AuxiliaryEngine

HDD Trucks Locomotive Ships

g/m

ile/to

n

Moving From Primary to Secondary Pollutants

• Ozone: only formed in atmosphere• Particulate matter: 80% formed in the

atmosphere

Mechanism DevelopmentBasic Lab.

DataTheory and Estimations

Chemical Characterization Instrumentation

Atmospheric Simulation

Experiments (Environmental Chamber Data)

Chemical Mechanism

Simulation of Experiments

Consistent?No

YesMechanism Might be satisfactory for air quality modeling

No

Environmental Chamber Research

Secondary Organic Aerosol (SOA) Formation

Particle Diameter (µm)0.01 0.3 2 10

Con

cent

ratio

nCondensation

Nucleation

Volatile OrganicCompound

HeterogeneousChemistry

Oxidation(OH,O3,NO3)

Fine Particles Coarse Particles

Evaporation

SOA Theory: Equilibrium Partitioning of Semi-Volatile Compounds

G1, G2,…,Gn

Kom,i =Ai/∆Mo

Gi

=MWomγipo

L,i

RT

HC + Oxidant αiPi Pi= Ai + Gi

oom

omo

i oiom,

iom,io

ii

o

MK1KαM

MK1Kα

MYΔHCMY

+=

+=== ∑∑

(Odum et al., 1996)

Ai – Aerosol Products

Gi – Gaseous Products

Mo – Mass of Organic in Aerosol

Kom – Gas Partitioning Coefficient

R – Ideal Gas Constant

γ – Activity Coefficient

poLi – Sub cooled saturation liquid vapor pressure

α – Mass based stoichiometric coefficient

Single Product Model

A1, A2,…,AiKom,i

UCR Chamber Facility

UC Riverside/CE-CERT Environmental Chamber

Dual 90 m3

Teflon reactors

Descending frames to maintain positive pressure

Purified air flushed 450 m3 enclosure

Injection and sample portsDual SMPS’s

Particle free two chamber humidifier

Air handler circulation system

TDMA – Hygroscopicity Measurement

Argon arc lamp

Black lights

SOA formation potential

∑∑ +===

i oiom,

iom,io

ii

o

MK1Kα

MYΔROGΔMY

0

2

4

6

8

10

12

0 100 200 300 400 500 600Time (minute)

Volu

me

(µm

3 /cm

3 )

0

10

20

30

40

50

60H

C (p

pb)

PM Volume(corrected)PM Volume(uncorrected)Hydrocarbon

∆RO

G

∆Mo

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0 50 100 150 200 250 300Mo(µg/m 3)

Mas

s Fr

actio

nal Y

ield

HCo:Nox>8.0

HCo:NOx<5.5

SOA Formation Potential (yield) as Function of Aerosol Mass (m-Xylene)

Traditional Smog Chamber Experiments

Typical Urban Mass Loadings

0

50

100

150

200

250

300

350

400

0 200 400 600 800 1000 1200 1400 1600 1800 2000ΔHC(µg/m3)

Mo(

µg/

m3 )

HCo:NOx>8.0

HCo:NOx<5.5

0

5

10

15

20

25

0 100 200 300ΔHC(µg/m3)

Mo( µ

g/m

3 )α1=0.049, Κ1=0.301α2=0.178, Κ2=0.008

α1=0.024, Κ1=0.229α2=0.152, Κ2=0.004

Aerosol Mass vs. Reacted HC

Detailed chemical speciation needed to identify key oxidation products; chemical mechanism based model needed to predict impacts of NOx and other atmospheric species on SOA formation

Semi-Empirical Model Estimates

High NOx

Low NOx

What can we do here?

• There are many individual and team projects that lead to the results shown above– What do the particles formed look like?

• What are their chemical characteristics?• What are their physical characteristics?• What is their atmospheric behaviour?

– What hazardous air pollutants are released?• By whom? Where? Who is impacted?

– Lots of instruments, lots of students to work with, lots of questions to address……

Chemical Instrumentation

+VOCs Oxidants

Products (aerosol)

Products (gases)

GC-FID

PTR-MS

IntermediatesLCMS

AMS

IR-CRDS

CRDS

Aerosol Instrumentation

Atmospheric reactor

SMPS(Size

Distribution)

CPC(Number

Concentration)

APM(Single

Particle Mass)

(CCN)Cloud particle activation

SOA

Aerosol Mass

Produced