The Chemistry of Smog
Robert Healy
The Atmosphere
Comprised of several
layers
 Troposphere contains the
air that we breathe

The Troposphere- Composition

~10miles in height

Contains most clouds

Many different gases

Organic Compounds (OCs)

OCs are essential ingredients for smog
formation
Manmade Sources of Organic
Compounds

Vehicle exhaust

Industrial
emissions

Biomass burning

eg benzene
Natural Sources of Organic Compounds

Vegetation

Trees

Rainforests

eg isoprene
Smog in the Troposphere

A “soup” of chemicals

Harmful to health

How is it formed?
Smog Formation
OCs + Nitrogen Oxides
SUNLIGHT
SMOG
What is in smog?
Smog Composition
SMOG

NO2
Ozone
Oxidised OCs

PARTICLES (nanosize)


benzene
phenol
Particles in the Troposphere

Air quality and health
effects

Affect climate…
..directly- scatter light
..indirectly- form clouds

Composition not
fully understood
Smog Chambers at UCC

Teflon Reactor

6000L volume

UV and Visible
lamps

VOCs oxidized to give gas phase
products and particles
Smog Chamber at PSI Zurich

27,000L Teflon vessel inside aluminium housing

VOCs oxidized in the presence of light

Gas products and particles formed
Typical Smog Chamber Experiment



Typical “banana plot” for VOC photooxidation
First particles appear 1hr after lights on…
..followed by rapid increase in number and size
Denuder-Filter Sampling
Denuder Tube
(gas collection)
Filter pack
(particle collection)
Air flow

Glass denuder

Gases stick to walls

Particles pass through to filter
Denuder Sampling
Denuder tube
Particle phase
Gas phase
Filter
Air Flow
Denuder Sampling at PSI

Denuder set up inside chamber

Filter is connected to denuder

Air is pumped through the denuder-filter
Microscope Images of Filters
NANOPARTICLES
BEFORE SAMPLING
AFTER SAMPLING
GC-MS Analysis

GC-MS can separate
and identify products

Gas products from
tube identified

Particle products from
filter identified
GC-MS Analysis
 TUBE
methacrolein
methylglyoxal
MVK

FILTEROH-carbonyls
glyoxal
C4 dicarbonyl

Some compounds are found both in the
gas and particle phase
Results and Impact

Denuder-filter method separates gases
and particles efficiently

Method is simple and cheap

GC-MS allows for successful identification
of products found in smog

Unexpected results…
Unexpected Results

Small products from reaction of OCs found in
particles

These are only expected in gas phase

Suggests “new” chemistry occurring in particles

Possible explanation- self-assembling polymers
+
=
Future Directions

Chamber experiments on benzene-like
compounds

Field measurements at different sites

Identification of new species in particles

Toxicology studies
Acknowledgments

Thanks to… CRAC LAB

everyone at
PSI

and…