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?
2
3
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
4
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
5
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)
6
Ideal Combustion
FUEL (HCs) + AIR (O2 & N2)
CO2 + H2O + N2
7
Typical Combustion
FUEL (HCs) + AIR (O2 & N2)
Unburned HCs + NOX + CO +
CO2 + H20
8
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
9
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)
10
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
11
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
12
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
13
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
14
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
15
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
16
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
17
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
18
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
19
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%
20
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)
21
22
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
23
Speed
IM240 Test
68
58
48
38
28
18
8
24
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
25
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
26
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
27
“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
28
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
29
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!
30
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
31