Analysis of Exposure to Residential Wood Combustion 

Emissions for Different Socio-Economic Groups

Revised Draft Report

Prepared by:

EC/R Incorporated

501 Eastowne Drive, Suite 250

Chapel Hill, NC 27514

EPA Contract No. EP-D-05-085

Work Assignment No. 4-3

Prepared for:

Gil Wood, Work Assignment Manager

Office of Air Quality Planning and Standards

U.S. Environmental Protection Agency

Research Triangle Park, North Carolina 27514

April 22, 2010
ii

Disclaimer

Although the analysis described in this document has been funded 

wholly or in part by the United States Environmental Protection 

Agency contract EP-D-05-087 to EC/R Incorporated, it has not 

been subject to the Agency's review and therefore does not 

necessarily reflect the views of the Agency, and no official 

endorsement should be inferred.
Contents

Tables iv

Figures iv

1. Introduction 1

2. Census Data and Calculation Methods 2

3. Calculation Methods 4

3.1 Racial and Ethnic Categories and the Total Population 4

3.2 Age Categories 5

3.3 Level of Education 6

3.4 Household Income 6

3.5 Poverty Level 7

4. Results 9

4.1 General Distribution of Risks for Different Population Subgroups 9

4.2 Populations Residing in Geographic Areas with High Levels of Risk from Residential 

Wood Smoke 17

4.3 Risks on Tribal Lands 17

5. References 22
iv

Tables

Table 1. Summary of Census Data used to Analyze Risks for Different Socio-economic

Groups 3

Table 2. Distribution of Inhalation Cancer Risk for Racial and Ethnic Groups 10

Table 3. Distribution of Risk for Different Age Groups 11

Table 4. Distribution of Risk for Adults with and without a High School Diploma 12

Table 5. Distribution of Risk for People Living in Households below the National Median 

Income and Below the Poverty Line 13

Table 6. Summary of Average Incremental Risks due to Residential Wood Smoke for Different 

Population Groups 14

Table 7. Use of Wood and Other Solid-Fueled Heating Equipment by Different Segments of the 

Population 16

Table 8. Populations in Geographic Areas with High Levels of Risk from Residential Wood 

Smoke 19

Table 9. Distribution of Risk for People Living on Tribal Lands 21

Figures

Figure 1. Comparison of Average Risks from Residential Wood Smoke for Different Population 

Groups 15

Figure 2. Tribal Lands 18

Figure 3. Census blocks with high incremental risk due to residential wood smoke emissions20
1

1. Introduction

This document describes the approach used to evaluate the cancer risks sustained by 

different social, demographic and economic groups due to emissions of hazardous air pollutants 

(HAP) from residential wood combustion. This work was carried out in support of the U.S. 

Environmental Protection Agency’s review of New Source Performance Standards for 

residential wood heaters. 

The National-scale Air Toxics Assessment (NATA) for 2002 estimated cancer risks due 

to the inhalation of residential wood combustion emissions.1 In the current analysis, these cancer 

risk estimates have been linked to detailed census data in order to evaluate the distribution of 

risks for different social, demographic and economic groups. The following population 

categories were studied:

Total population

White

African American (or Black)

Native Americans

Other races and multiracial

Hispanic or Latino

Children 18 years of age and under

Adults 19 to 64 years of age

Adults 65 years of age and over

Adults without a high school diploma

Households earning under the national median income

People living below the poverty line

The NATA results for a particular census block reflect the level of risk that would be 

experienced by an individual residing in the block for 70 years. The NATA risk estimates used 

in this analysis have not been adjusted for commuting patterns or for the difference between 

indoor and outdoor pollutant concentrations. 

Risk estimates from residential wood combustion were compared to the overall inhalation 

risks experienced by the same population categories. The overall inhalation risk estimates

include HAP emissions from all stationary sources, onroad and nonroad mobile sources, 

dispersed area sources, and the background due to long-range transport and natural emissions.

Section 2 of this report describes the census data used in this analysis. Section 3 presents 

the algorithms used to compute the distributions of risk and exposure, and Section 4 presents 

results of this analysis. Census data on the ownership of residential wood combustion equipment 

by different population subcategories are also presented in Section 4.
2

2. Census Data and Calculation Methods

Table 1 summarizes the census data used in this analysis, showing the source of each 

dataset and the level of geographic resolution. All of the data are from the 2000 Decennial 

census. Race and ethnicity data were obtained at the census block level. Age distributions, data 

on educational status, and economic data were obtained at the block group level. A census block 

contains about 50 people on average; and a block group contains about 26 blocks on average, or 

about 1,350 people. (For comparison, a census tract is larger than a block group, with each tract 

containing an average of 3 block groups, or about 4,300 people.)

Table 1. Summary of Census Data used to Analyze Risks for Different Socioeconomic Groups

Type of population category Source of data

Level of 

geographic 

resolution

Racial and ethnic categories Landview® Census block

Age groups SF3 Table P8 Block group

Level of education - adults without a high 

school diploma

SF3 Table 37 Block group

Households earning below the national 

median income

SF3 Table 52 Block group

People living below the poverty line SF3 Table P87 Block group

Data on race and ethnicity were obtained primarily from the Landview® database 

compiled by the Census Department.2 Landview® gives a breakdown for the population of each 

census block among different racial classifications, including: White, African American or 

Black, American Indian or Native Alaskan, Asian, Native Hawaiian or other South Pacific 

Islander, other race, and two or more races. In the current analysis, the Asian, Native Hawaiian 

or other South Pacific Islander, and other race categories were combined into a single category. 

The Landview® database also indicates the number of people in each tract that are of Hispanic 

or Latino ethnicity. Landview® covers the 50 states, the District of Columbia, and Puerto Rico, 

but does not cover the Virgin Islands. Race and ethnicity data on the Virgin Islands were 

obtained from the Virgin Islands Summary File.

3

Data on age distributions, poverty status, household incomes, and education level in the 

U.S. and Puerto Rico were obtained from the 2000 Census of Population and Housing Summary 

File 3 (SF3) Long Form. For the U.S. this file was accessed on a DVD version prepared by 

GeoLytics.4 SF3 data for Puerto Rico were obtained from the Census Department website,

5

 and 

data for the Virgin Islands were retrieved from similar tables in the Virgin Islands Summary 

File.3
3

The SF3 data set consists of over 800 separate tables, each providing information on a 

different subject. For the current analysis, data were obtained from Tables P8, P37, P52, and 

P87. Table P8 gives the estimated numbers of men and women in different age categories for 

each census block group. Table P37 analyzes the level of education attained by men and women 

over 25 years of age (e.g. some high school but no high school diploma, high school graduate, 

some college, etc.). Table P52 gives information on household income in 1999, and Table P87 

estimates the number of people living below the poverty line in each block group. 
4

3. Calculation Methods

NATA estimates the average cancer risk from residential wood combustion for each 

census tract. For the current analysis, this risk estimate was assumed to apply to all individuals 

residing in the tract. We used census identification codes to link the NATA modeling results for 

each tract to the appropriate census statistics for all of the census blocks within the tract. This 

allowed us to estimate the numbers of people falling into different population subcategories 

within each block. We then analyzed the distribution of estimated inhalation risks within each 

population subcategory, giving the numbers of people within the subcategory that are exposed to 

different risk levels. Each distribution involved a tabulation of all of the census tracts affected 

by residential wood combustion emissions. We also computed the average risk for all 

individuals in each population subcategory. For comparison, distributions of risk and average 

risks were computed for all NATA emissions. 

Section 3.1 describes the calculation method used for categories where block-level data 

were available -- racial and ethnic categories and the total population. Sections 3.2 through 3.5 

describe calculation methods for age categories, education status, household income, and poverty 

status, respectively. 

3.1 Racial and Ethnic Categories and the Total Population

Since race and ethnicity data were available at the census block level, the calculation of 

risk distributions for these categories involved a simple block-by-block accumulation of the 

people in each subcategory. We began by identifying a set of bins reflecting the level of risk. 

The population of each block was then assigned to the appropriate risk bin based on the modeled 

risk level in the block. The numbers of people in each risk bin were then added together for all 

of the blocks modeled for the residential wood combustion category:

H(Rab,s) = ∑i

(Ra≤Ri<Rb) [N(s,i)] (1)

where:

H(Rab,s) = the population count for risk bin Rab, which is between Ra and Rb for population 

subgroup “s”

Ri = the modeled risk level in block “í” (estimated lifetime cases of cancer per 

million population)

∑i

(Ra≤Ri<Rb) refers to the summation over all blocks i where Ri falls in bin Rab, between Ra

and Rb

N(s,i) = the number of people within population subcategory s, in block i

The same approach was used for the total population. The average risk for a given population 

subcategory or for the total population was calculated using the following equation:

A(S) = ∑i [N(s,i) × Ri] ∕ ∑i [N(s,i)] (2)
5

where:

A(s) = the average risk for population subgroup “s” (estimated lifetime cases of cancer 

per million population)

∑i refers to the summation over all blocks “í” modeled for the emission source 

category

N(s,i) and Ri were defined above

It must be noted that in the overall NATA risk analysis, only stationary sources were 

modeled at the census block level. Risks due to onroad and nonroad mobile emissions sources, 

dispersed area sources, and ambient background levels of HAP were analyzed at the census tract 

level instead of the block level. EPA chose this larger scale of analysis for these categories for 

two reasons. First, the locations of these sources are not known definitively. Rather, the 

geographic distribution of emissions for these categories has been estimated from county level 

emissions data. Second, emissions from these categories are believed to be more uniformly 

distributed within a given county or census tract. Therefore, in the current analysis, we have 

assumed that the NATA risks for mobile sources, area sources, and background pollutant levels 

are the same for all blocks within a given census tract. As noted above, stationary source risk 

estimates were available at the census block level. 

3.2 Age Categories

Age data were retrieved from the Table P8 of the census SF3 Table, which contains data

on the numbers of males and females of different ages in each census block group. In processing 

the age data, we began by aggregating the categories in the census to the broader age groups 

studied in this analysis. For instance, the total number of children 18 years of age and under was 

calculated by adding together the number of girls under 1 year, the number of boys under 1 year, 

the number of 1-year-old girls, the number of 1-year-old, and so on up to and including 18-yearold girls. In this way, we calculated the number of children age 18 and under, the number of 

adults from 18 to 64, and the number of adults 65 and older in each census block group.

The next step was to estimate the numbers of people in each age group at the block level. 

To make this calculation, we assumed that the fraction of people in each age group was the same 

for all blocks in a given block group. Thus, the number of people in a particular age group and 

within a particular census block was estimated as follows: 

N(a,b/bg) = N(t,b/bg) × N(a,bg) ∕ N(t,bg) (3)

where:

N(a,b/bg) = number of people within age group “a”, in block “b” of block group “bg”

N(t,b/bg) = total number of people in block “b” of block group “bg”

N(a,bg) = number of people within age group “a” in block group “bg”

N(t,bg) = total number of people in block group “bg”
6

Equation 1 was then applied to the block-level population estimates to generate risk distributions 

for different age groups, and Equation 2 was used to compute the average risk for each age 

group.

3.3 Level of Education

Table P37 of the SF3 dataset specifies the education status for men and women age 25 

and older for each census block group, based on the last grade completed. To obtain the total 

number of adults without a high school degree, we added together the numbers who had 

completed grades below a high school senior. Thus, the number of people without a high school 

degree equals the sum of the number of males with no schooling, the number of females with no 

schooling, the numbers of males and females who have completed nursery school through 4th

grade, up to the numbers of males and females who have completed some high school but not 

received a high school degree.

The number of adults without a high school degree as a fraction of the total population 

was assumed to be the same for each block in the block group. Thus, the number of adults 

without a high school degree in each block was computed as follows:

N(nhs,b/bg) = N(t,b/bg) × N(nhs,bg) ∕ N(t,bg) (4)

where:

N(nhs,b/bg) = number of adults without a high school diploma, in block “b” of block group 

“bg”

N(t,b/bg) = total number of people in block “b” of block group “bg”

N(nhs,bg) = number of adults without a high school diploma in block group “bg”

N(t,bg) = total number of people in block group “bg”

Equation 1 was then used to generate risk distributions based on the block-level results, and 

Equation 2 was used to compute the average risk for adults without a high school diploma. 

3.4 Household Income

Table P52 of the SF3 dataset estimates the numbers of households in each block group 

with income for the year 1999 in various ranges, generally divided into $5000 increments (e.g. 

$10,000 to $14,999, $15,000 to $19,999, etc.). The median national income for 1999 was about 

$42,000 per year. Therefore, in order to determine the number of households with incomes 

under the median income, we added the estimates for the ranges below that level. We assumed 

that the household incomes in the $40,000 to $44,999 increment were evenly distributed over 

this range. Therefore, 40% of the households in the $40,000 to $49,000 income range were 

assumed to be below the national median income of about $42,000. The following equation was 

used to estimate the fraction of households below the national median income within each census

block group:

F(sm,bg) = [C<10 + C10-15 + .... + C35-40 + (0.4×C40-45)] ∕ CT (5)
7

where:

F(sm,bg) = fraction of households in block group “bg” with incomes below the median 

national income

C<10 = number of households with incomes under $10,000

C10-15 = number of households with incomes from $10,000 to $14,999

C35-40 = number of households with incomes from $35,000 to $39,999

C40-45 = number of households with incomes from $40,000 to $44,999

CT = total number of households in block group “bg”

The fraction of people living in households below the median income for each block 

within the block group was assumed to the same as the fraction of households below the median 

income for the block group.

N(sm,b/bg) = F(sm,bg) × N(t,b/bg) (6)

where:

N(sm,b/bg) = number of people in block “b” of block group “bg” living in households below 

the national median income

F(sm,bg) = fraction of households in block group “bg” below the national median income

N(t,b/bg) = total number of people in block “b” of block group “bg”

Equation 1 was then used to generate risk distributions based on the block-level results, and 

Equation 2 was used to compute the average risk for adults without a high school diploma. It 

must be noted that this approach neglects any potential relationship between household size and 

income level within a particular block group. However, it is expected to provide a reasonable 

indication of the risk level of people living below the national median income, relative to the 

population as a whole. 

3.5 Poverty Level

Table P87 of the SF3 dataset estimates the total number people in each block group living 

below the poverty level, as well as the numbers of people below the poverty level in different age 

groups. The current study did not include an analysis of poverty status by age group, only of the 

total population below the poverty line. The fraction of people below the poverty line was 

assumed to be the same for each block in the block group. Thus, the population below the 

poverty line in each block was computed as follows:

N(p,b/bg) = N(T,b/bg) × N(p,bg) ∕ N(T,bg) (7)

where:

N(p,b/bg) = number of people below the poverty line in block “b” of block group “bg”

N(T,b/bg) = total number of people in block “b” of block group “bg”

N(p,bg) = number of people below the poverty line in block group “bg”

N(T,bg) = total number of people in block group “bg”
8

Equation 1 was then used to generate risk distributions based on the block-level results, and 

Equation 2 was used to compute the average risk for the population living below the poverty 

line. 
9

4. Results

Cancer risks due to residential wood smoke emissions to ambient air have been evaluated

for various segments of the general population and for geographic regions of concern. 

Section 4.2 analyzes the distribution of risks among different socioeconomic and age groups on a 

national average basis. Section 4.2 analyzes the risks for different population groups living in 

census tracts which are estimated to be impacted by particularly high levels of residential wood 

smoke, and Section 4.3 analyzes the estimated risks for populations living on Tribal Lands.

4.1 General Distribution of Risks for Different Population Subgroups

Table 2 shows the distribution of estimated lifetime inhalation cancer risks due to the 

inhalation of residential wood smoke in ambient air for different racial and ethnic groups.

Distributions of risk are shown for different age groups in Table 3; and for adults with and 

without a high school diploma in Table 4. Finally, Table 5 shows the estimated distribution of 

risk for people living in households below the national median income, and for people living 

below the poverty line. Each of the tables includes histograms showing the numbers of people in 

the different population subgroups that are exposed to different risk levels, along with the 

calculated average nationwide risk estimates for the population subgroups. For comparison, each 

of the tables also show the distributions of total inhalation risks for all sources of HAP, including 

point sources, onroad and nonroad mobile sources, dispersed area sources, and the background 

due to long-range transport and natural emissions. Table 6 and Figure 1 summarize the national 

average risk levels for the different population subgroups.

The risk estimates in Tables 2 through 6 and Figure 1 are based on the 2002 NATA 

analysis. It must be noted that the risk estimates are for inhalation of residential wood smoke 

which has been emitted to ambient air, and do not include indoor emissions in the houses where 

wood-burning equipment is used. The estimated inhalation risks reflect the level of risk that 

would be experienced by an individual residing in the block for 70 years. In addition, the risk 

estimates are not adjusted for commuting patterns or for the difference between indoor and 

outdoor pollutant concentrations. 

Tables 2 through 6 and Figure 1 indicate that, on a nationwide basis, cancer risks due to 

residential wood smoke emissions among disadvantaged population groups generally are lower 

than the risks for the general population due to residential wood smoke emissions. The 

exception is the population over 65 years of age, who are exposed to an average cancer risk 

about 5% higher than the general population. This 5% difference is probably not significant 

given the large uncertainties of emissions estimates, population exposure estimates, and risk 

analyses. Nonetheless, these results for the population over 65 follow the same pattern as the 

available census statistics for the ownership of wood combustion equipment. As shown in 

Table 7, people age 65 and over are more likely than the general population to use wood and 

other solid fuel burning equipment as their primary source of household heating.6 African 
Total 

population White

African 

American

Native 

American

Hispanic or 

Latinoc

Other and 

multiracial

Total 

population White

African 

American

Native 

American

Hispanic 

or Latinoc

Other and 

multiracial

0 to 1 192,127,500 141,072,833 24,196,345 1,901,306 32,740,752 24,956,919 67.3 65.8 69.0 76.4 83.8 75.0

1 to 5 70,992,721 54,946,102 9,143,004 473,130 4,994,337 6,430,485 24.9 25.6 26.1 19.0 12.8 19.3

5 to 10 12,876,802 10,627,814 1,140,260 67,995 726,463 1,040,733 4.5 5.0 3.3 2.7 1.9 3.1

10 to 20 7,542,158 6,367,228 507,438 32,133 488,792 635,359 2.6 3.0 1.4 1.3 1.3 1.9

20 to 30 948,071 831,369 21,168 7,574 63,643 87,960 0.3 0.4 0.1 0.3 0.2 0.3

30 to 40 630,273 507,518 30,084 5,255 53,745 87,416 0.2 0.2 0.1 0.2 0.1 0.3

40 to 50 201,553 169,802 5,384 1,858 13,269 24,509 0.1 0.1 0.0 0.1 0.0 0.1

50 to 100 20,045 17,035 190 264 2,759 2,556 0.0 0.0 0.0 0.0 0.0 0.0

Total number exposed 285,339,123 214,539,701 35,043,873 2,489,515 39,083,760 33,265,937 100.0 100.0 100.0 100.0 100.0 100.0

1.65 1.77 1.28 1.18 0.94 1.35

0 to 20 9,969,267 8,458,432 191,185 542,767 1,024,347 776,833 3.5 3.9 0.5 21.8 2.6 2.3

20 to 30 64,074,767 55,430,705 4,146,292 744,065 7,299,008 3,753,658 22.5 25.8 11.8 29.9 18.7 11.3

30 to 40 84,510,869 69,220,887 8,542,175 471,433 7,456,367 6,276,374 29.6 32.3 24.4 18.9 19.1 18.9

40 to 50 61,432,040 44,201,640 9,688,501 294,581 7,566,317 7,247,318 21.5 20.6 27.6 11.8 19.4 21.8

50 to 100 59,932,337 34,481,074 11,834,925 390,096 13,496,368 13,226,242 21.0 16.1 33.8 15.7 34.5 39.8

100 to 150 4,889,341 2,393,756 589,290 42,917 2,124,443 1,863,378 1.7 1.1 1.7 1.7 5.4 5.6

150 to 200 433,112 278,212 41,423 2,804 108,420 110,673 0.2 0.1 0.1 0.1 0.3 0.3

200 to 250 41,090 28,158 4,855 458 5,377 7,619 0.0 0.0 0.0 0.0 0.0 0.0

250 to 300 6,007 5,557 156 15 133 279 0.0 0.0 0.0 0.0 0.0 0.0

300 and over 50,293 41,280 5,071 379 2,980 3,563 0.0 0.0 0.0 0.0 0.0 0.0

Total number 285,339,123 214,539,701 35,043,873 2,489,515 39,083,760 33,265,937 100.0 100.0 100.0 100.0 100.0 100.0

42 40 48 36 51 54

Notes:

Table 2. Distribution of Inhalation Cancer Risk for Racial and Ethnic Groups

Overall modeled inhalation risk 

from all NATA sources

Numbers of people in different ranges for lifetime cancer riskb

Average risk (chances in one 

million)

Modeled risk from residential 

wood combustion

Range of lifetime individual 

cancer risk (chance in one 

million)a

Average risk (chances in one 

million)

Percentagess of people in different ranges for lifetime cancer riskb

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and not adjusted for exposure factors.

bDistributions by race are based on demographic information at the census block level. Risks from point source emissions were modeled at the block level, as were other NATA stationary 

source emissions. Wood combustion emissions and all other non-point sources, including mobile sources, area sources, and background risks were analyzed at the census tract level in NATA. 

c

The Hispanic or Latino population is double-counted in this analysis, since different individuals within the category may classify themselves as White, African American, Native American, or 

other.
Total 

population Ages 0 thru 18

Ages 19 thru 

64

Ages 65 and 

up

Total 

population

Ages 0 

thru 18

Ages 19 

thru 64

Ages 65 

and up

0 to 1 192,127,500 53,046,269 115,759,579 23,321,652 67.3 68.7 67.1 65.7

1 to 5 70,992,721 18,556,872 43,279,148 9,156,700 24.9 24.0 25.1 25.8

5 to 10 12,876,802 3,231,691 7,873,739 1,771,372 4.5 4.2 4.6 5.0

10 to 20 7,542,158 1,953,343 4,565,455 1,023,360 2.6 2.5 2.6 2.9

20 to 30 948,071 243,958 590,476 113,638 0.3 0.3 0.3 0.3

30 to 40 630,273 157,884 394,077 78,312 0.2 0.2 0.2 0.2

40 to 50 201,553 49,927 127,006 24,619 0.1 0.1 0.1 0.1

50 to 100 20,045 5,419 13,004 1,621 0.0 0.0 0.0 0.0

Total number 285,339,123 77,245,364 172,602,485 35,491,274 100.0 100.0 100.0 100.0

1.65 1.59 1.67 1.72

0 to 20 9,969,267 2,830,464 5,685,041 1,453,762 3.5 3.7 3.3 4.1

20 to 30 64,074,767 17,500,952 37,959,277 8,614,538 22.5 22.7 22.0 24.3

30 to 40 84,510,869 23,008,476 51,008,006 10,494,387 29.6 29.8 29.6 29.6

40 to 50 61,432,040 16,527,823 37,373,043 7,531,175 21.5 21.4 21.7 21.2

50 to 100 59,932,337 15,942,166 37,132,689 6,857,482 21.0 20.6 21.5 19.3

100 to 150 4,889,341 1,338,519 3,076,448 474,374 1.7 1.7 1.8 1.3

150 to 200 433,112 75,702 303,204 54,207 0.2 0.1 0.2 0.2

200 to 250 41,090 7,603 29,183 4,304 0.0 0.0 0.0 0.0

250 to 300 6,007 1,097 3,974 935 0.0 0.0 0.0 0.0

300 and over 50,293 12,563 31,620 6,110 0.0 0.0 0.0 0.0

Total number 285,339,123 77,245,364 172,602,485 35,491,274 100.0 100.0 100.0 100.0

42 42 43 41

Notes:

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and not adjusted for exposure factors.

Overall modeled inhalation risk from 

all NATA sources

Table 3. Distribution of Risk for Different Age Groups

Average risk (chances in one 

million)

Percentages of people in different ranges for 

lifetime cancer riskb

bDistributions by age and education level are based on modeling data at the Census block level, and age and education data at the block group level. 

All blocks in a block group are assumed to have the same age and income distribution.

Modeled risk from residential wood 

combustion

Range of lifetime individual cancer 

risk (chance in one million)a

Numbers of people in different ranges for lifetime cancer 

riskb

Average risk (chances in one 

million)
Total 

population

Total age 25 and 

older

Age 25+ without 

a high school 

diploma

Total 

population

Total age 25 and 

older

Age 25+ without 

a high school 

diploma

0 to 1 192,127,500 123,342,859 26,512,819 67.3 66.8 72.3

1 to 5 70,992,721 46,624,966 7,872,176 24.9 25.2 21.5

5 to 10 12,876,802 8,566,616 1,350,847 4.5 4.6 3.7

10 to 20 7,542,158 4,982,279 758,850 2.6 2.7 2.1

20 to 30 948,071 615,927 83,998 0.3 0.3 0.2

30 to 40 630,273 421,182 59,613 0.2 0.2 0.2

40 to 50 201,553 136,480 19,829 0.1 0.1 0.1

50 to 100 20,045 11,685 2,332 0.0 0.0 0.0

Total number 285,339,123 184,701,993 36,660,464 100.0 100.0 100.0

1.65 1.68 1.39

0 to 20 591,970 6,485,429 1,247,986 1.6 3.5 3.4

20 to 30 3,859,397 41,674,890 9,215,444 10.7 22.6 25.1

30 to 40 7,829,994 54,772,175 9,302,229 21.8 29.7 25.4

40 to 50 8,233,739 39,884,291 6,915,063 22.9 21.6 18.9

50 to 100 13,715,812 38,445,631 8,880,870 38.1 20.8 24.2

100 to 150 1,464,630 3,061,977 1,024,391 4.1 1.7 2.8

150 to 200 152,391 313,131 63,272 0.4 0.2 0.2

200 to 250 103,171 28,593 5,098 0.3 0.0 0.0

250 to 300 15,590 4,389 833 0.0 0.0 0.0

300 and over 7,825 31,487 5,278 0.0 0.0 0.0

Total number 35,974,519 184,701,993 36,660,464 100.0 100.0 100.0

42 42 44

Notes:

Percentages of people in different ranges for lifetime 

cancer riskb

Table 4. Distribution of Risk for Adults with and without a High School Diploma

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and 

not adjusted for exposure factors.

Overall modeled inhalation risk 

from all NATA sources

Average risk (chances in one 

million)

bDistributions by age and education level are based on modeling data at the Census block 

level, and age and education data at the block group level. All blocks in a block group are 

assumed to have the same age and income distribution.

Range of lifetime individual cancer 

risk (chance in one million)a

Numbers of people in different ranges for lifetime 

cancer riskb

Modeled risk from residential wood 

combustion

Average risk (chances in one 

million)
Total 

population

In households 

below the 

national median 

incomec

Below the 

poverty line

Total 

population

In households 

below the 

national median 

incomec

Below the 

poverty line

0 to 1 192,127,500 98,510,096 26,985,443 67 70 73

1 to 5 70,992,721 33,003,551 7,873,375 25 23 21

5 to 10 12,876,802 5,885,471 1,371,892 5 4 4

10 to 20 7,542,158 3,324,768 750,935 3 2 2

20 to 30 948,071 449,313 101,598 0 0 0

30 to 40 630,273 303,955 71,432 0 0 0

40 to 50 201,553 99,634 21,563 0 0 0

50 to 100 20,045 14,036 4,790 0 0 0

Total number 285,339,123 141,590,823 37,181,029 100 100 100

1.65 1.55 1.40

0 to 20 9,969,267 5,957,656 1,433,983 3 4 4

20 to 30 64,074,767 35,942,526 9,059,840 22 25 24

30 to 40 84,510,869 38,772,677 8,857,266 30 27 24

40 to 50 61,432,040 27,559,127 7,012,564 22 19 19

50 to 100 59,932,337 30,180,471 9,592,666 21 21 26

100 to 150 4,889,341 2,911,401 1,127,686 2 2 3

150 to 200 433,112 216,229 82,580 0 0 0

200 to 250 41,090 19,908 5,460 0 0 0

250 to 300 6,007 3,245 746 0 0 0

300 and over 50,293 27,583 8,238 0 0 0

Total number 285,339,123 141,590,823 37,181,029 100 100 100

42 42 45

Notes:

Modeled risk from residential wood 

combustion

Table 5. Distribution of Risk for People Living in Households below the National Median Income and Below the Poverty Line

Range of lifetime individual cancer 

risk (chance in one million)a

Numbers of people in different ranges for lifetime 

cancer riskb

Percentages of people in different ranges for 

lifetime cancer riskb

Overall modeled inhalation risk from 

all NATA sources

c

The median income is the national median household income in 1999, about $41,000.

Average risk (chances in one 

million)

Average risk (chances in one 

million)

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and not adjusted for exposure factors.

bDistributions by income are based on modeling data at the Census block level, and income data at the block group level. All blocks in a block 

group are assumed to have the same age and income distribution.
Population group

From 

residential 

wood smoke

From all 

NATA sources

Total population 1.65 42

Racial and ethnic groups

White 1.77 40

African American 1.28 48

Native American 1.18 36

Hispanic or Latino 0.94 51

Other and multiracial 1.35 54

Age groups

Ages 0 thru 18 1.59 42

Ages 19 thru 64 1.67 43

Ages 65 and up 1.72 41

Education status

Total age 25 and older 1.68 42

Age 25 and older without a high school diploma 1.39 44

Poverty status

People in households below the national median income 1.55 42

People below the poverty line 1.40 45

Notes

Table 6. Summary of Average Risks due to Residential Wood Smoke for Different 

Population Groups

Average cancer risk (chances 

in one million)a

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and not 

adjusted for exposure factors.
15

Figure 1. Comparison of Average Risks from Residential Wood Smoke for Different Population Groups.
Heating equipment

Total 

populationAfrican 

American Hispanic

Elderly 

(65 and 

over)

Main heating equipmenta

Heating stove 0.85 0.23 0.41 0.92

Fireplaces with inserts 0.15 0.06 0.05 0.22

Fireplaces without inserts 0.05 0.01 0.05 0.07

Cooking stove 0.09 0.13 0.36 0.23

Subtotalb

1.14 0.44 0.87 1.44

Supplemental heating equipmenta

Heating stove 2.04 0.38 0.44 2.27

Fireplaces with inserts 4.30 2.04 1.94 3.91

Fireplaces without inserts 4.80 3.65 4.04 3.71

Cooking stove 0.05 0.02 0.07 0.07

Subtotalb

11.18 6.09 6.49 9.96

Total main and supplementalb

12.32 6.53 7.36 11.40

a

Includes all solid fuels: wood, coal, pellets, etc.

b

Totals may include some double counting of households that use different types of 

equipment

Use of equipment by households in different 

population groups (percentage of the group 

using the equipment)

Table 7. Use of Wood and Other Solid-Fueled Heating Equipment by 

Different Segments of the Population
17

Americans and Hispanic Americans are less likely to use wood and other solid fuel burning 

equipment than the general population, either as their primary source or as a supplementary 

source of household heating. (Information is not available on the use of wood burning or solid 

fuel burning equipment by economic status or education level.)

4.2 Populations Residing in Geographic Areas with High Levels of Risk 

from Residential Wood Smoke

The overall average cancer risk from residential wood smoke emissions is about 1.65 in a 

million, on a nationwide average for the general population. About 9.3 million people are 

exposed to risk levels of 10 or more in a million, about 950 thousand to risk levels of 20 or more 

in a million, about 630 thousand at 30 or more in a million, about 200 thousand at 40 or more in 

a million, and about 20,000 at 50 or more in a million. Figure 2 shows the locations of the 

census tracts exposed to these higher risk levels from residential wood smoke. Table 8 shows 

the makeup of populations in these census tracts. The table shows that, in general, the that the 

fractions of people living below the national median income and people living below the poverty 

line are higher than average in tracts where the risk from residential wood smoke emissions is 50 

or more in a million. However, the fractions of people in these categories are roughly the same 

as the average for the nation as a whole for tracts where the risk from residential wood smoke 

emissions is 10 to 50 in a million. In addition, the fractions of other disadvantaged groups are 

not higher than average in the higher-risk tracts.

4.3 Risks on Tribal Lands

Figure 3 shows the location of Tribal Lands in the U.S. 7 Table 9 summarizes the 

distribution of risk levels from residential wood smoke for people living in census blocks with 

centroids located on Tribal Lands. The table compares these risks to the risk levels for all Native 

Americans living on and off Tribal Lands and to the overall population in the nation as a whole. 

In addition, Table 9 shows the distributions of total inhalation risks for all sources of HAP, 

including point sources, onroad and nonroad mobile sources, dispersed area sources, and the 

background due to long-range transport and natural emissions. Table 9 shows that the average 

risk from residential wood smoke is lower for people living on Tribal Lands than for the general 

population, and lower than the average risk for all Native Americans living on and off of Tribal

Lands. 
 

 

   

       

  

 

 

   

 

 

  

                 

   

 

   

  

 

 

 

  

   

        

 

   

 

 

  

 

            

 

  

 

     

 

  

         

 

   

         

 

 

 

  

       

 

 

         

  

 

 

     

  

    

     

       

 

 

     

  

      

        

 

 

 

    

 

 

     

 

    

      

    

  

  

   

 

     

                  

	

          

	








Population group

Risk of 10 or 

more in a 

milliona

20 or more 

in a 

milliona

30 or more 

in a 

milliona

40 or more 

in a 

milliona

50 or more 

in a 

milliona

Racial and ethnic groups

White 84 85 82 84 85 75

African American 6 2 2 1 1 12

Native American 1 1 1 1 1 1

Hispanic or Latino 7 7 8 7 14 14

Other and multiracial 9 11 13 12 13 12

Age groups

Ages 0 thru 18 26 25 25 25 27 27

Ages 19 thru 64 61 62 63 63 65 60

Ages 65 and up 13 12 12 12 8 12

Education status

Total age 25 and older 66 66 67 67 58 65

Age 25 and older without a high school diploma 10 9 10 10 12 13

Poverty status

People in households below the national median income 45 48 49 51 70 50

People below the poverty line 10 11 11 12 24 13

Number of people in the high-risk tracts 9,342,100 1,799,942 851,871 221,598 20,045 9,342,100

Notes:

Prevalence of the population group in census tracts with 

relatively higher risk due to residential wood combustion (%)

Prevalence in 

the nation on 

average (%)

Table 8. Populations in Geographic Areas with High Levels of Risk from Residential Wood Smoke

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration and not adjusted for exposure factors.
	


All people on 

Tribal Lands

Native 

Americans 

on Tribal 

Lands

All Native 

American

Total 

population

0 to 1 716,089 462,028 1,901,306 192,127,500

1 to 5 185,838 40,165 473,130 70,992,721

5 to 10 8,912 2,117 67,995 12,876,802

10 to 20 2,820 92 32,133 7,542,158

20 to 30 7,574 948,071

30 to 40 5,255 630,273

40 to 50 1,858 201,553

50 to 100 264 20,045

Total number exposed 913,659 504,402 2,489,515 285,339,123

0.73 0.29 1.18 1.65

0 to 20 544,728 357,444 542,767 9,969,267

20 to 30 227,889 119,248 744,065 64,074,767

30 to 40 76,143 16,715 471,433 84,510,869

40 to 50 55,409 6,866 294,581 61,432,040

50 to 100 8,045 3,179 390,096 59,932,337

100 to 150 1,445 950 42,917 4,889,341

150 to 200 2,804 433,112

200 to 250 458 41,090

250 to 300 15 6,007

300 and over 379 50,293

Total number 913,659 504,402 2,489,515 285,339,123

22 20 36 42

Notes:

Table 9. Distribution of Risk for People Living on Indian Lands

aModeled risks are for a 70-year lifetime, based on the predicted outdoor concentration 

and not adjusted for exposure factors.

Range of lifetime individual 

cancer risk (chance in one 

million)a

Modeled risk from residential 

wood combustion

Average risk (chances in one 

million)

Overall modeled inhalation risk 

from all NATA sources

Average risk (chances in one 

million)

Numbers of people in different ranges for lifetime cancer 

risk
22

5. References

1. EPA. 2008. National Air Toxics Assessments. U.S. Environmental Protection Agency, 

Research Triangle Park, NC. http://www.epa.gov/ttn/atw/natamain/

2. Census. 2002. LandView 5 on DVD [electronic resource] : a viewer for EPA, Census 

and USGS data and maps. U.S. Census Bureau, Washington, D.C.

3. Census. 2008. Virgin Islands Summary File. U.S. Census Bureau, Washington, D.C. 

www.factfinder.census.gov

4. Census. 2004. Census DVD 2000 Long Form SF3, Release 2.2. Geolytics, Inc., East 

Brunswick, NJ. www.geolytics.com

5. Census. 2008. SF3 Data for Puerto Rico. U.S. Census Bureau, Washington, D.C. 

www.factfinder.census.gov

6. Census. 2008. American Housing Survey – 2007.

7. Location of Tribal Lands within the U.S. Geographic Information Systems Shapefile 

obtained from Laura McKelvey, U.S. Environmental Protection Agency.