Mobile Sources.ppt
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Transcript Mobile Sources.ppt
Mobile Sources
Lydia Scheer
ITEP
Overview
What are mobile sources?
What are the pollutants of concern from mobile
sources?
How are mobile sources regulated?
How do we quantify emissions and assess
impacts from mobile sources?
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Mobile Source Categories
On-Road
Light/medium-duty passenger vehicles
Heavy-duty trucks and busses
Motorcycles
Non-Road
Construction and farm equipment
Lawn and garden equipment
Marine vessels
Aircraft
Recreational vehicles & hobby engines
Industrial and commercial equipment
Railway equipment and locomotive
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Mobile Sources & Pollution
On-road sources contribute >25% of TOTAL air pollution
Passenger cars more fuel efficient, but number of total vehicles
increasing rapidly
Fuel economy is being traded for vehicle size and performance
Non-road sources contribute 15-20% of TOTAL air
pollution
Previously not regulated as heavily as motor vehicles
Specialized engines, fewer emissions controls, etc.
Motorcycle emissions can be more significant than passenger vehicles
even though more fuel efficient
Aircraft engines primary emitters of ambient lead from mobile sources
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Mobile Source Emissions
Exhaust: by-products of fuel combustion process
Evaporative: losses from in-line leakage
Fugitive Dust: brake dust, tire wear, etc.
Sometimes accounted for in mobile source modeling
Re-entrained road dust & refueling losses quantified with
AREA sources (paved/unpaved roads & gas stations)
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Ideal Combustion
FUEL (HCs) + AIR (O2 & N2)
CO2 + H2O + N2
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Typical Combustion
FUEL (HCs) + AIR (O2 & N2)
Unburned HCs + NOX + CO +
CO2 + H20
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Evaporative Emissions
HC/VOC pollutants escape to air through fuel
evaporation
Hot engine & exhaust system vaporize gasoline
Leaks in seals, fuel lines, or components
Evaporation rate increases with temperature and
in presence of sunlight
Prime conditions for ground-level ozone formation
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Mobile Source Pollutants & Their
Contribution to Ambient Air Pollution
Carbon monoxide (CO) - 82%
Oxides of nitrogen (NOx) - 56%
Carbon Dioxide (CO2) – 47%
HAPs - 50%
Volatile Organic Compounds (VOCs) - 45%
PM - 13-15% (PM10 & PM2.5)
Lead (Pb) - 13%
SO2 - <5%
Data include emissions from all mobile sources.
Source: EPA National Air Quality and Emissions Trends Report (2003
Special Studies Edition)
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Exhaust Pollutant:
Carbon Monoxide (CO)
Product of incomplete combustion
Occurs when carbon in fuel is only partially oxidized
Odorless, colorless gas with dangerous health effects
Reduces flow of oxygen in bloodstream (binds to hemoglobin)
Affects mental functions and visual acuity
People with heart disease are particularly susceptible
Recent concerns about CO-related deaths from boating
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Exhaust Pollutant:
Nitrogen Oxides (NOx)
Form under high pressure & temperature
conditions in engine
Nitrogen and oxygen atoms form various nitrogen
oxides
NO2 gives smog its brownish color
Precursors to ozone formation
Contribute to formation of acid rain
Can cause or accentuate respiratory problems
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Exhaust Pollutant:
Carbon Dioxide (CO2)
Product of “ideal” combustion
Does not directly impair human health at typical ambient
levels
”Greenhouse gas” (GHG) contributes significantly to
potential for global warming
Also: methane, nitrous oxide and fluorocarbons
Over 30% of all US GHG emissions from mobile sources
(majority from on-road sources)
Increase in GHG emissions from transportation 2x more
than average increase in other sectors
New GHG standards applied to new (2012) light-duty &
heavy-duty vehicles
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Exhaust Pollutants: PM & SOx
Particulate Matter (PM)
Not a significant concern for most mobile sources
Majority of emissions from diesel engines
Other contributors of particle pollution
Fugitive dust (brakes/tires)-primarily PM10
Secondary formation of aerosolized particles (HC, NOx, SOx
chemical reactions in atmosphere)
Oxides of Sulfur (SOx, SO2)
Not a significant concern for most mobile sources
Majority of emissions from diesel engines
Significant reductions in sulfur content of fuel contributing to
reduced emissions
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Exhaust Pollutant: Lead (Pb)
Lead as a fuel additive phased out in mid-70s
Drastic change in Lead emissions from mobile sources
1980: 87% of all source emissions
2000: 13% of all source emissions
2000: 96% mobile source lead emissions from aircraft
Lead concentrations (ug/m3)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1980
1985
1990
1995
2000
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Exhaust Pollutant:
Air Toxics/HAPs
Air Toxics primarily considered carcinogenic
(cancer-causing)
Many air toxics are VOCs and/or hydrocarbons
(HCs)
EPA estimates mobile source air toxics emissions
account for 50% of all cancers attributed to
outdoor sources of air toxics
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Exhaust Pollutant:
Air Toxics/HAPs (cont.)
At least 21 different
compounds found in vehicle
exhaust
Some compounds present in
unburned gasoline; others a
result of incomplete
combustion
Benzene and Diesel PM (DPM)
are of greatest concern from
mobile sources
Revised standards (2007)
significantly lowered benzene
content of gasoline (33%+)
Diesel PM filter systems can
reduce PM emissions up to 90%
Acetaldehyde
Acrolein
MTBE
Diesel Particulate Matter (DPM)
Polycyclic Organic Matter (POM)
Ethylbenzene
Naphthalene
Arsenic Compounds
Formaldehyde
Nickel Compounds
Benzene
Hexane
1,3-Butadiene
Lead Compounds
Styrene
Chromium Compounds
Manganese Compounds
Toluene
Dioxin/Furans
Mercury Compounds
Xylene
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Diesel Exhaust Emissions
Diesel engines are typically more fuel efficient
Diesel emissions contain less CO and CO2, significantly more
PM, NOx & SO2 than standard gasoline
Exhaust is damaging to lung tissue & more carcinogenic than
gasoline exhaust
Highest concern: school busses & areas with heavy truck/bus
traffic and/or idling
New standards to cut emissions up to 95% (ultra-low sulfur
fuel) took effect June 1, 2010
Biodiesel (vegetable or animal fat-derived) is a suitable
substitute for petro-diesel with significantly lower emissions
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Regulating Automobile Emissions
CAA of 1970 gave EPA broad authority to regulate
motor vehicle pollution
Title II of CAA addresses mobile sources
Fundamental engine design improvements reduced
emissions
More stringent emissions limits, more efficient control
technologies enacted over the years
Constant “battle” with automobile & oil industries,
collectors/hobbyists
2012 CAFE standards increased to 34.1 combined mpg
average for passenger cars/trucks
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Emission Controls
Catalytic converter (1975)
Uses a series of heavy metals to reduce and/or oxidize pollutants
Made ineffective by lead (Pb) leads to phase-out of leaded
gasoline
3-way catalyst (1981)
Oxidizes CO & HCs CO2 & H2O
Reduces NOx elemental N & O
May produce hydrogen sulfide (H2S) as a by-product
Oxygen sensor
Optimizes catalytic converter’s efficiency
Repairing faulty oxygen sensor can improve fuel efficiency up to
40%
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Emission Controls (cont.)
Engine vapor recovery system
Recycles evaporative emissions from engine compartment to be
used as fuel source
On-board diagnostic system (OBDS)
Monitors vehicle emissions and engine performance
Alerts driver of problem (“check engine light”)
Diesel Retrofits
Particulate filters (tailpipe) – most effective at curbing emissions
Oxidation Catalysts (tailpipe)
Closed crankcase ventilation filters (improve in-cab levels)
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Inspection & Maintenance (I/M)
National policy set by EPA enforced in over 40
metropolitan areas
Inspections must take place at
Government or private inspection stations that do not perform
vehicle repairs
Licensed service stations & repair shops
Annual checks required
Enhanced I/M - “IM240” tailpipe test
Emissions measured while vehicle driven on dynamometer at
changing speeds—replicates “typical” driving habits
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Speed
IM240 Test
68
58
48
38
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Complimenting Technologies
Remote sensing
“Snapshot” of exhaust emissions
Cannot measure evaporative emissions
Measures ratio of CO (& exhaust HC) to CO2
“The Smart Sign”—Denver, CO
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Assessing Impacts from Mobile
Sources: Modeling
MOVES (MOtor Vehicle Emission Simulator)
Encompass all pollutants (including greenhouse gases) and all mobile
sources at the a variety of scales
Replacement for MOBILE6 and NONROAD models
NMIM (National Mobile Inventory Model)
Desktop computer application used to estimate emissions for on-road
and non-road sources
Uses current versions of MOBILE6 and NONROAD to calculate EIs based
on multiple user-defined scenarios
Can be used to calculate national, individual state, or county inventories
Other models for specific applications such as fuel composition and
implementation costs, etc.
More information: http://www.epa.gov/otaq/models.htm
Tools & Calculators:
http://www.epa.gov/otaq/stateresources/tools.htm
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Assessing Impacts from Mobile
Sources: Inventories
AP-42 Emission Factors based on MOBILE5 modeling
estimates
Data compiled by State/Local agencies available
Emission Factors for mobile sources rely on:
Vehicle-Miles Traveled (VMT) estimates for on-road sources
Hours of operation and/or number of vehicles/engine types for
non-road sources
Emissions estimates for your county/area
Average emissions estimates for surrounding area applied to
reservation based on land base and/or population
Collect your own VMT and hours of operation & use emission
factors from State
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“Cleaner” Fuels
Reformulated gasoline (RFG) introduced in 10
smoggiest cities (1995)
Oxygenated gasoline additives
Ethanol, MTBE, ETBE, etc.
Improve fuel efficiency & reduce some emissions
(VOCs & CO) – less ozone formation
Can be harmful to health and environment in
other ways
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What can you do?
Maintain vehicle properly
Poorly maintained vehicles can pollute up to 10 times more than
well-maintained ones
<10% of cars contribute nearly half of all hydrocarbon emissions
Don’t tamper with emissions controls
Combine trips, carpool, or share rides
Avoid traveling during high-traffic times
Observe speed limits and/or reduce speed
Consider alternative fuels
Pave or maintain roads
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What We Just Covered
Mobile Sources include on-road and non-road sources
Mobile Sources are one of the leading contributors to air
pollution
Primary pollutants of concern: CO, NOx, HCs and other
Air Toxics
Modeling and Emissions Inventories aid in assessing
impacts from mobile source pollution
Advances in technology and more stringent regulations
are “helping”
Pollution from mobile sources is hard to control because
WE LOVE OUR CARS!
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Resources
Alternative fuels and vehicles
http://www.afdc.energy.gov/afdc/
http://www.epa.gov/greenvehicles
http://www.fueleconomy.gov/
Mobile Source Modeling and Inventories
http://epa.gov/otaq/models.htm
CAA Title II
http://www.epa.gov/air/caa/title2.html
http://www.epa.gov/air/caa/peg/
Mobile Source Regulatory Milestones
http://www.epa.gov/otaq/invntory/overview/solutions/milestones.htm
Air Pollution Trends
http://www.epa.gov/air/airtrends/index.html
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