Air Pollution in Los
Angeles:
History & Overview
Prof. Suzanne Paulson
Department of Atmospheric and
Oceanic Sciences & Institute of
Environment and Sustainability
Director, UCLA Center for Clean Air
Air Pollution has a Long
History
Earliest written records of air pollution begin in
at least 65 BC.
 Mention of air pollution increased steadily as
society developed.
 The first air pollution regulation was probably
issued in 1273, when King Edward I forbid coal
burning near the White Castle.

Air Pollution Has Been
Around for a Long Time
Mid 1600s John Evelyn: “It is evident … that
near half of the children that are born
and bred in London die under two
years of age (a child born in a country
village has an even chance of living
near forty years) ...the constant and
unremitting poison is communicated
by the foul air, which, as the town
grows still larger has made regular
and steady advances in its fatal
influence.”
Air Pollution Directly from Sources
Becomes Hard to Ignore

1930: Meuse Valley, Belgium, 63 dead, 600 injured.
The 15-mile valley trapped pollutants released by coke
ovens, steel mills, blast furnaces, zinc smelters, glass
factories, and sulfuric acid plants.

1948 Donora, Pennsylvania, USA – This industrial
valley experienced a four-day air pollution episode
that resulted in 20 deaths, 600 ill, and 1400 seeking
medical attention. Out of a population of 14,000.
These happened in Winter Time
1952 London, five-day winter episode resulted
in 12,000 excess deaths + many illnesses.
What is an excess death? Who died?
Between the Early 1950’s and Now, Many
More ‘Air Pollution Disasters’ have
Happened, but Most Have Been Milder.

London, 1956, Similar winter meteorology leads to
“only” 700 deaths. New regulations were already
helping.

New York City Thanksgiving 1966: 168 people died
during a strong temperature inversion.
We’ll discuss temperature inversions later
Los Angeles Smog: a Whole
New Story

It happens in summer, not winter. Began in the 1940s.
Low visibility from summer time smog is blamed for
2000 car accidents in one day 1954.
Los Angeles had lots of agriculture, and
crop yields were dropping fast.
Los Angeles smog is
similar to winter
smogs, but it is
whiter, and contains
high levels of ozone.
Particles: Size Matters
PM10 = All particles smaller than 10 microns in
Diameter. Mostly from stuff being ground up.
PM2.5 = All particles smaller than 2.5 microns in
Diameter. Mostly from combustion.
TSP: Total
Suspended
Particulate =
Everything you
can catch on a
filter
Where Particles Deposit Depends on Their
Size
Movememt of ultrafine particles
along sensory neurons 
(neurodegeneration)
Coarse Particles, > 2.5 microns
Deposit in upper airways, where they are removed by
cilia but likely exacerbate Asthma
Transfer of ultrafines to circulatory
system
0.1 micron < Fine particles < 2.5 microns
Penetrate into Alveoli. Body cannot remove them.
Small Particles are visible!


Old Federal Standard: PM 10 below 150 g/m3
for 24 hrs and 50 g/m3 annual average.
Newest Federal Standard: PM 2.5 below 65
g/m3 for 24 hrs and 12 g/m3 annual average.
PM2.5 particles scatter light very efficiently,
especially particles that are between 0.2 and 1
microns
Air Pollutant Types and
Sources
{
Wintertime vs. Summertime Smog
Types of Air Pollution

Primary pollutants are emitted directly from
sources.
Particulate Matter (PM), Carbon monoxide, Lead,
sulfur dioxide, nitrogen dioxide, many “air toxics”
 London, Beijing, California’s central valley, New
Delhi


Secondary pollutants form in the atmosphere from
chemical transformations of the primary
pollutants.
 Ozone, particulate matter, some nitrogen
dioxide, some air toxics
 Los Angeles, Mexico City, Santiago Chile
Criteria Pollutants
-Pollutants for which there are national
ambient air quality standards (NAAQS) In
the US the criteria pollutants are:
 Carbon monoxide
CO
 Lead
Pb
 Oxides of nitrogen
NOx
 Ozone
O3
 Sulfur dioxide
SO2
 Particulate matter
PM10/PM2.5
Combustion makes more
than just CO2 and water
fuel + Air 
Carbon dioxide + water +
VOCs + NOx + particulate
matter (PM), Carbon Monoxide
(CO), SO2, Pb, toxic organics as
benzene, polyaromatic
hydrocarbons, acrolein etc.
Pollutant Sources: NOx from
Combustion, VOCs from Everything


NOx: All combustion sources  NOx

Vehicles, Industry, Biomass Burning
NOx is essentially all from human activities
Hydrocarbons (HCs or VOCs or ROGs) come from
many sources:

Vehicles (both the engine and leaking unburned
fuel)

Industrial and Residential: solvents, paints &
coatings, cleaners

Trees
Small particles (PM2.5 and PM0.1) are
from combustion or smog chemistry,
large particles (PM10) are from
mechanical grinding.

Particles:
All combustion sources  fine and
ultrafine particles
Vehicles, Industry, Biomass Burning

Industrial processes  dust and fumes
 Roadways, agriculture, deserts and
desertification  dust

Formation of Los Angeles
Style Smog
The “Air Quality Index” (AQI) is defined
as the percent of the Ambient Air
Quality Standard (Usually National or
World Health Organization’s)
{
Formation of Smog- LA Style
VOCs + NOx + sunlight
 photochemical smog
(= O3 , more particles
and other nasty
compounds)
The Daily Smog Cycle
VOCs
VOC
reaction
products
Ozone
CO is emitted directly from sources—no
photochemistry, so it shows where most of
the pollution sources are.
http://www.epa.
gov/airnow/
mapselect.html
http://www.airn
ow.gov/index.cf
m?action=airno
Days Exceeding Standard
Stage 1 Smog Alert
Old Fed. Standard 1-hr, 120 ppb
2008 8 hr std 75 ppb
250
200
150
100
50
0
197619801984 1988
1992
1996 2000 2004
2008 2012
Year
OZONE IN LOS ANGELES 1976-2014
(There is a new ozone standard 12/2014: 70 ppb over 8 hrs)
PM 2.5
2002
2013
Air Pollution
Then and Now
1950’s
Now
Population
4.8 Million
16 Million
Vehicles
2.3 Million
11 Million
Peak Ozone Levels
680 ppb
160 ppb
Peak CO Levels
33 ppm
4.7 ppm
Peak NO2 Levels
690 ppb
110 ppb
Peak PM10 Levels
649 g/m3
84 g/m3
Peak PM2.5 Levels
unknown
65 g/m3
75+ % Reduction of most pollutants!
Emissions have been reduced by more than 90%.
Schedule for meeting Federal
Air Quality Standards
Pollutant
Target Attainment
Status
Schedule
CO:
2000
Actually met in 2003
PM10:
2006
Actually met in 2010.
Ozone-1-hr:
was 2010 Current target: 2022
PM2.5:
2018
Maybe.
8-Hr Ozone:
2040?
Why some places have good
air quality and others have
bad air quality
{
Ingredients for poor air
quality
Large amounts of pollution emissions.
Cars, industry, trucks, dust, agricultural
burning, wildfires….

Summer time smog requires sunlight

Low winds, temperature inversions.


“the solution to pollution is dilution”
Temperature Inversions
Wind flow in Los Angeles on typical
(smoggy) days
Daily smog cycle in Los Angeles
Daytime mixing height limitations in
Los Angeles
Temperature profile of the lower atmosphere
When it is well mixed
The atmosphere cools with increasing
altitude, at an average of 6.5 degrees C
per km.
Pretend an air parcel is
a contained in a
weightless, elastic
balloon containing a
fixed amount of air. As
the balloon’s altitude
increases, the balloon
will expand, and its air
temperature will cool.
If the local temperature profile matches the normal rate of cooling
for air parcels, there is no reason for parcels to prefer one height or
location over another. The parcels can move around freely.
Temperature profile of the lower atmosphere
When when mixing is poor
An inversion is a temperature profile that is constant or
increasing with increasing height. This puts warm air over
cool air, and stops upward mixing completely.
Causes of Inversions
1. Radiation Inversions: These are common
almost everywhere
The average atmosphere is warmest
near the surface, but locally the
temperature profile can be
different.
 After sunset, the earth's surface
cools and radiates energy, so the air
closest to the surface cools before
air higher up.
 An inversion forms - air near surface
cooler and denser than the air
above it. These inversions are most
common and strongest on winter
mornings.

Diurnal evolution of the nocturnal surface
inversion and daytime mixed layer.
Unlike the daytime “mixed layer”, the nighttime surface layer is very
poorly mixed. Pollutants stay at the level where they were emitted,
and move laterally  bad pollution
Radiation Inversions in Valleys
In the evening and night, the ground surface cools. If the
ground is not flat, the cooled air will flow down hill, and
accumulate in the valley. The air will be trapped there until the
sun comes out and warms up the ground.
Sometimes the cold weather persists for days, and pollution
accumulates day after day. This is usually the reason extreme
pollution events (London, Beijing, Denora) happen when they
do.
Measuring plumes from freeways in the early morning:
Weak winds from the north of the freeway dominate in the
early AM. (They reverse during the day)
_________________________________________________
The Imprint of the Freeway is Many Times Larger During
Just
Before Sunrise Compared to Daytime
_________________________________________________
1
Pre-Sunrise: Winter
Pre-Sunrise: Summer
Daytime (Zhu et al 2002b)
Relative UFP Concentration
Kansas
0.8
Pico
0.6
Pearl
Ocean Park
Donald Douglas
0.4
Olympic
Palms
0.2
Freeway
Upwind
0
-1500
-1000
-500
Downwind
0
500
1000
1500
Distance from Freeway (m)
2000
2500
3000
2. The Trouble with Beautiful
Weather: Subsidence Inversions
High pressure systems produce large areas of subsiding
air. As the air descends, it is compressed and heats up.
Subsidence inversions are large enough to cover entire
regions, and persist for days to weeks. They are common
in many places, especially Los Angeles.
When the weather is fair, there is almost
always an upper level inversion
3. Marine Inversions
On sunny days, the land surface heats and causes air to
rise. Marine air is pulled in to fill the void, and the marine
air is cooler, resulting in cold air under air warm air.
Inversion Types – Los Angeles has Four!
1) Radiation inversions.
2) Subsidence inversions.
3) Cool marine air undercuts warm air over land, resulting
in a marine inversion.
4) Flow of air from a high plateau descends and warms by
compression, creating a cap above a cooler air mass in a
basin below the highlands.
The mixing height changes with season; it is
lowest in the winter
Cleaning up the air
Regulatory Authority

South California Air Quality Management District
(SCAQMD): Local industrial and commercial
sources.

California Air Resources Board (CARB):
passenger vehicles, consumer products, local
diesel vehicles & construction equipment.

Federal: Interstate sources; planes, trains,
interstate trucks & busses

International: Large marine vessels and
international airliners
Major Steps to Cleaning
up Air in LA
State Actions: Mobile Sources
Because California has such a large economy, if it
requires lower emissions from cars than the
USEPA, automakers cannot ignore it. In the end,
California has almost always succeeded in setting
the regulations it wants.
 1961 The first automotive emissions control
technology in the nation, Positive Crankcase
Ventilation, is mandated.
 1978 Mandate 3-way catalysts control
hydrocarbons, nitrogen oxides, and carbon
monoxide.

State Actions: Mobile Sources
1984 first smog check program; this will be
updated repeatedly.
 1990-current Mandated improvements to the
durability of emissions control
 1990-current Mandate low and Zero Emission
Vehicles.
 Vehicles on the road today are 100 to 400 times
cleaner than vehicles in the 1960s. And some
vehicles have zero emissions.

State Actions: Gasoline
Clean fuels are probably the closest we can get
to a “silver bullet”. Clean the gasoline, and all of
the cars use it right away.
 1976, 1992 CARB limits then removes lead.
 1992 & 1996 Phase I & Phase II California Cleaner
Burning Gasoline introduced. Reduces volatility,
reactivity and toxicity of gasoline, and made
major improvements to 1 hr ozone
concentrations.
 Winter 1992, ARB requires addition of
oxygenates to cut CO emissions by 10%. (MTBE
was added, to be replaced later by ethanol).

State Actions: Fuel Delivery &
Diesel fuel
1972, 1976, 1991 Vapor recovery at gas stations
in San Diego, Polluted areas, and then the whole
state
 1993 First California Diesel Fuel comes to
market. Lowers diesel particulate emissions by
14 tons/day, sulfur dioxide by 80 tons/day and
nitrogen oxides by 70 tons/day emissions.
 2006 Ultra-low sulfur diesel is introduced

State & Local Actions: Consumer
Products, Small Engines
California has many reformulated products.
These include household cleaners, insect sprays,
bbq lighter fluid, and paints.
 CARB and SCAQMD have implemented multiple
programs for small engines such as gardening
equipment and small boats.
 CARB and SCAQMD worked with other
stakeholders to clean up the ports: clean trucks,
port and dock electrification

Federal (National) Actions
1963 First Federal Clean Air Act. The act has
been amended many times, often tightening
National Ambient Air Quality Standards (NAAQS)
 1967 New federal Clean Air Act gives California
special authority to set its own emissions
standards for new vehicles.
 1970 U.S. Environmental Protection Agency (U.S.
EPA) created.
 2000’s USEPA works with CARB to create clean
trucks program, finally addressing this major
source of pollution.

Socio-Political Climate
1940’s, 1950’s, 1960’s there were many protests
related to air quality in Los Angeles
 Rachel Carson writes Silent Spring
 1940s-1980s Candidates for Governor all went to
visit the Universities to discuss air pollution
control.
 1970
First Earth Day. Earth Day is still observed
every April.
 1973 OPEC Oil Embargo raises the price of oil.
Market forces result in more fuel efficient
automobiles and industry, and corresponding
lower air emissions.

Local: SCAQMD Control of stationary
sources, monitoring, planning, education
1993 adopts Regional Clean Air Incentives Market
(RECLAIM) program for NOx and SOx. VOCs were
considered, but VOCs are far more complicated.
 Runs the extensive air quality monitoring network;
handles permitting for point and area sources
 .Holds public hearings, ~150 educational events each
year
 Agencies (especially SCAQMD) perform special studies
for communities when needed.

California’s Regulatory Approach:
Industry
California agencies (CARB and SCAQMD) expect
best available control technologies at a
minimum.
 CARB often works to set policies that are
technology forcing.
 Policies are developed with input from
stakeholders, including the industry to be
regulated, but also representatives of NGOs, the
public and other interested parties.
 California has been sued repeatedly for its
policies. This typically delays implementation.

New Policies in the mid ‘10s
Most of the low hanging fruit has been picked. Also
emphasis on climate – air quality co-benefits
More improvements in engine design and emissions
control durability.
 Tighter requirements for consumer products
 Require new glass in autos to keep them cooler
 Cash for clunkers, trade in programs for gardening
equipment
 “Mode shifting” to encourage use of
transit/walking/cycling
 Further improvements in the ports and goods shipment
 Emphasis on growing the zero emissions market,
including Hydrogen, electric vehicles, fuel cell vehicles

Los Angeles still has a very long way to go
With existing
to control ozone
controls
Thank you