10.4 Accidental Vegetation Fires

10.4.1 Emissions

Introduction

Category 1580 is an area source category that accounts for criteria pollutant (particulate, organic, NOx, SOx, and CO) and greenhouse gas emissions (Biogenic-CO2, CH4, and N2O) from wildfires in woodland, timber, brush and grass.

Carbon Dioxide emissions from this category are considered to be biogenic emissions. Biogenic Carbon Dioxide (Bio-CO2) emissions are a subset of total CO2 emissions which are emitted from materials that are derived from living cells, excluding fossil fuels, limestone and other materials that have been transformed by geological processes. Bio-CO2 originates from carbon that is present in materials such as wood, paper, vegetable oils and food, animal, and yard waste.

Planned or prescribed fires such as weed burning, field crops, prunings, range improvement burning and forest management are covered in categories 315-319.

Methodology

Methodology for this category is in accordance with the California Air Resources Board’s (CARB’s) document “Methods for Assessing Area Source Emissions in California” for the Wildfires. Activity data (acreage burnt) estimates were obtained from the California Department of Forestry and Fire Protection (CDF) and CARB. Wildfire emissions are calculated using the Geographic Information System (GIS) based Emission Estimating System (EES) model developed for ARB by UC Berkeley’s Center for the Assessment and Monitoring of Forest and Environmental Resources (CAMFER) laboratory. Wildfire footprint is overlaid on vegetation landcover map, calculating the amount of each fuel consumed in the fire. Fuel loading is assigned for each fuel component that makes up the vegetation type.

Emission factors and vegetation acreage consumed vary from fire season to fire season depending on type of vegetation consumed and weather conditions. For example, average composite emission factors and amounts of acreage burnt in the Bay Area by county are shown below for year 2008 2011.

Table 10.10: Composite emission factors (lb/acre).
category PM TOG NOx SO2 CO CH4 N2O CO2bio
#1580 Accidental Vegetation Fires 229 237 76 23 2158 86 4.43 385.4
Table 10.11: Acreage burned.
Alameda Contra Costa Marin Napa San Francisco San Mateo Santa Clara Solano Sonoma Total
798 249 200 757 11 249 290 964 249 3767

Other sources for the vegetation combustion emissions related information are the U.S. Department of Energy’s (DOE’s) Energy Information Administration (EIA); the Environmental Protection Agency’s (EPA’s) document AP-42, and the California Energy Commission (CEC).

County Distribution

County distribution of emissions is based on acreage burnt in each of the San Francisco Bay Area counties.

Table 10.12: County fractions.
category ALA CC MAR NAP SF SM SNC SOL SON
#1580 Accidental Vegetation Fires 21.2% 6.6% 5.3% 20.1% 0.3% 6.6% 7.7% 25.6% 6.6%

Monthly Variation

On the basis of historical data, the California Department of Forestry and Fire Protection (CDF) suggests most of the wild fires occurring from mid-May to mid-November. The percentage of wild fires by month is estimated as follow: May - 5%, June - 10%, July - 15%, August - 20%, September - 25%, October - 20% and November - 5%.