An emission inventory is an itemized list of
emission estimates for sources of air pollution in a given area for a
specified time period. Present and future year inventories are critical
components of air quality planning and modeling. The ultimate goal of
the planning process is to identify and achieve emission patterns that
do not result in violations of ambient air quality standards.
Emissions are calculated by
BAAQMD staff using various procedures. Emission computation methodology
by source category is outlined in the BAAQMD publication, "Source Category
Methodologies." The BAAQMD participates in the California Emission Inventory
Technical Advisory Committee (EITAC) and maintains the best available
inventory methodologies.
The emission inventory is divided
into stationary, mobile, and biogenic sources.
Stationary
Source Emissions
Stationary sources are further divided into point and area sources.
-
Point Sources
Sources identified on an individual facility basis or as a single
source are called point sources. Refineries and industrial plants
are examples of point sources. The emission characteristics of individual
facilities vary widely and each facility is examined individually.
The Permit Services Division of the BAAQMD collects and maintains
a computer data bank with detailed information on point sources. Almost
all facilities emitting greater than 2.5 tons/year of any air pollutant
are included. The District data bank contains information for about
4,000 facilities.
Data on the activity, seasonal variations,
and hours of operation are collected from each facility. Parameters
which affect the quantity of emissions are updated regularly. Emissions
are calculated using detailed data for each of the facilities by various
processes. The emissions from combustion and other general processes
are computed using generalized or specific emission factors. These
factors are periodically reviewed and updated.
-
Area Sources
Stationary sources not identified individually are called area sources.
This term is sometimes extended to cover groups of numerous small
point sources, such as dry cleaners or gas stations. Area sources
also include the diverse, unpermitted small sources which individually
do not emit significant amounts of pollutants but which together make
an appreciable contribution to the emission inventory. Examples of
area sources are residential heating and use of paints, varnishes,
and consumer products. Emissions from these sources are grouped into
categories and calculated based on surrogate variables. Information
on these surrogates is usually available for the state or by county.
Selected surrogates are used to apportion the category emissions into
diurnal and spatial patterns. Emissions for some source categories
are estimated by the California
Air Resources Board (ARB) based on statewide data.
Many area source categories are further classified
into subcategories for better emission computation, specification,
regulation development, and future-year projections. For example architectural
coating categories are subdivided into various types of coatings and
varnishes to account for varying solvent content. There are more than
800 different subcategories used in this inventory. Emissions for
categories affected by regulations are adjusted to reflect the controls
required and the estimated rule effectiveness achieved.
Mobile Source Emissions
Mobile sources consist of on-road motor vehicles and other mobile sources.
-
On-Road Motor Vehicles
On-road motor vehicles consist of passenger cars, trucks, buses and
motorcycles. Emissions from on-road motor vehicles are a major portion
of the emission inventory and are estimated using computer models
developed by ARB. These are referred to as EMFAC and BURDEN, the latest
available version, EMFAC2002 v2.2 was used in this inventory.
-
Other Mobile Sources
These sources include boats and ships, trains, aircraft, garden, farm
and construction equipment. Various methodologies are used to estimate
emissions from these sources. Emission factors and methodologies for
these sources are provided by ARB and EPA. Aircraft mix and activity
data specific to each airport are used in estimating emissions at
airports.
Biogenic
Sources
In addition to man-made air pollution, there are significant quantities
of pollutants from natural sources such as plants, animals, marshes, and
the earth itself. Vegetation for example, emits large amounts of isoprene,
terpenes, and other organic compounds, which are precursors of ozone.
Reactive organic emissions from Bay Area vegetation total about 170 tons
per day. The emission estimates are developed using a personal computer
version of the Biogenic Emissions Inventory System (BEIGIS) developed
by the California
Air Resources Board (ARB).
Planning
Inventory
A planning inventory is a seasonal inventory representing emissions when
a pollutant's concentrations are at their highest levels. For example,
the emission inventory for the ozone season represents emissions occurring
during the summer season, when ozone levels are highest. The emission
inventory for the carbon monoxide season represents emissions occurring
during the winter season, when carbon monoxide levels are highest. The
seasonal inventories (summer and winter) are prepared according to ARB
guidelines.
Table I and Table II contain
general statistics for the Bay Area as well as individual county statistics,
including population and total area. Light-duty vehicle population, as
well as estimated vehicle miles traveled (VMT) and total gasoline sales
are also included. VMT figures were obtained from the EMFAC2002 v2.2 mentioned
above.
Table III shows total daily
summer 2005 ozone planning emissions.
Table IV shows percent contribution from major groups of source categories.
BAAQMD staff work continually to update the emission inventory. More detailed
information and estimates for additional years have been included in Section
2 of the San
Francisco Bay Area Ozone Strategy for the 1-Hour National Ozone Standard
published in January 2006. More detailed emission data are available to
the public upon request. Updates on some individual source categories
may also be available. Some public requests may involve a charge; this
is usually the case if significant staff time, copying, or computer work
is required.
Greenhouse Gas
Emissions
The
District has also prepared an emission inventory of pollutants contributing
to climate change, or greenhouse gases (GHG). The Greenhouse Gas Source
Inventory estimates direct emissions from sources within the District’s
jurisdiction for the following gases: carbon dioxide, methane, nitrous
oxides, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.
This GHG Source
Inventory does not report indirect emissions, for example emissions associated
with electricity that is consumed in the Bay Area but produced outside
of the region. These indirect emissions are of interest to communities
developing GHG reduction strategies, and that seek to identify their total
“carbon footprint”. The District is working with ICLEI and other organizations
to assist communities in calculating both direct and indirect emissions.
Click here to view
the Source Inventory of Bay Area
Greenhouse Gas Emissions.
Table I
Growth in Population and Number of Light-Duty Vehicles
San Francisco Bay Area |
|
1990 |
1995 |
2000 |
2005 |
2010 |
2015 |
2020 |
Total Population* (1000's) |
5883 |
6250 |
6618 |
6910 |
7219 |
7534 |
7868 |
Total Vehicles ** (1000's) |
3301 |
3667 |
4033 |
4450 |
4800 |
5165 |
5554 |
Vehicles per 100 people |
56 |
59 |
61 |
64 |
66 |
69 |
71 |
Table II
2005 San Francisco Bay Area County Statistics |
County |
Population
(1000s) |
Area
(Square Miles) |
Daily Natural
Gas Usage***
(million cu.ft.) |
Daily
Gasoline Sales
(1000's gal.) |
Daily
Vehicle Miles Traveled**
(Millions) |
Land |
Water |
Total |
Alameda |
1,517 |
738 |
84 |
822 |
143 |
1,714 |
31.4 |
Contra Costa |
1,016 |
720 |
82 |
802 |
817 |
1,111 |
23.1 |
Marin |
251 |
520 |
308 |
828 |
24 |
332 |
6.1 |
Napa |
134 |
754 |
35 |
789 |
11 |
163 |
2.9 |
San Francisco |
798 |
47 |
185 |
232 |
139 |
953 |
10.5 |
San Mateo |
723 |
449 |
292 |
741 |
68 |
940 |
18.9 |
Santa Clara |
1,750 |
1291 |
13 |
1305 |
184 |
2,102 |
40.7 |
Solano* |
302 |
370 |
64 |
434 |
48 |
334 |
6.4 |
Sonoma* |
419 |
664 |
4 |
668 |
29 |
485 |
8.5 |
Total |
6,910 |
5,553 |
1,067 |
6,620 |
1,463 |
8,135 |
148.6 |
Table III
Total Bay Area Summer Average Emissions (tons/day) for 2005 |
Particulate
Matter <10 Microns
PM0 |
Reactive
Organic Gases
ROG |
Nitrogen
Oxides
NOx |
Sulfur Dioxides
SO2 |
Carbon
Monoxide
CO |
225 |
400 |
538 |
64 |
2,140 |
Table IV
Percent Distribution of Bay Area Summer Emissions 2005 |
|
Percent |
PM10 |
ROG |
NOx |
SO2 |
CO |
Petroleum Refining Processes |
0.4 |
2.2 |
0.1 |
44.6 |
0.1 |
Other Industrial/Commercial Processes |
7.4 |
2.9 |
0.5 |
14.6 |
0.1 |
Organic Compounds Evaporation |
-- |
23.2 |
-- |
-- |
-- |
Combustion |
4.9 |
1.5 |
11.1 |
18.7 |
3.8 |
On-Road Motor Vehicles |
4.5 |
35.7 |
51.2 |
3.9 |
64.9 |
Off-Highway Mobile Sources |
5.4 |
14.8 |
29.0 |
15.2 |
23.9 |
Aircraft |
0.3 |
1.7 |
4.4 |
1.2 |
2.2 |
Consumer Products and Other Sources |
77.2* |
17.9 |
3.5 |
1.7 |
5.1 |
TOTAL |
100 |
100 |
100 |
100 |
100 |
Contacts
Amir Fanai afanai@baaqmd.gov
|