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. Author manuscript; available in PMC: 2015 Nov 5.
Published in final edited form as: J Allergy Clin Immunol. 2014 Nov 5;134(5):1028–1035. doi: 10.1016/j.jaci.2014.09.029

Cost of near-roadway and regional air pollution-attributable childhood asthma in Los Angeles County

Sylvia Brandt 1, Laura Perez 2,3, Nino Künzli 2,3, Fred Lurmann 4, John Wilson 5, Manuel Pastor 5, Rob McConnell 5
PMCID: PMC4257136  NIHMSID: NIHMS631619  PMID: 25439228

Abstract

Background

Emerging evidence suggests that near-roadway air pollution (NRP) exposure causes childhood asthma. Associated costs are not well documented.

Objective

We estimated the cost of childhood asthma attributable to residential NRP exposure and regional ozone (O3) and nitrogen dioxide (NO2) in Los Angeles County. We developed a novel approach to apportion the costs between these exposures under different pollution scenarios.

Methods

We integrated results from a study of willingness to pay to reduce the burden of asthma with studies of health care utilization and charges to estimate the costs of an asthma case and exacerbation. We applied those costs to the number of asthma cases and exacerbations due to regional pollution in 2007 and to hypothetical scenarios of a 20% reduction in regional pollution in combination with a 20% reduction or increase in the proportion of the total population living within 75m of a major roadway.

Results

Cost of air pollution-related asthma in Los Angeles County in 2007 was $441 million for O3 and $202 million for NO2 in 2010 dollars. Cost of routine care (care in absence of exacerbation) accounted for 18% of the combined NRP and O3 cost and 39% of the combined NRP and NO2 cost—costs not recognized in previous analyses. NRP-attributable asthma accounted for 43% (O3) to 51% (NO2) of the total annual cost of exacerbations and routine care associated with pollution. Hypothetical scenarios showed that costs from increased NRP exposure may offset savings from reduced regional pollution.

Conclusions

Our model disaggregates the costs of regional pollution and NRP exposure and illustrates how they might vary under alternative exposure scenarios. The cost of air pollution is a substantial burden on families and an economic loss for society.

Keywords: air pollution, asthma, cost of illness, urban growth, vehicle emissions, willingness to pay

Introduction

Approximately 36 million people in the U.S. live within 300 feet of a four-lane highway, railroad, or airport.1 Emerging evidence suggests that near-roadway air pollution (NRP) exposure causes childhood asthma.2,3,4,5 A causal relationship implies that any subsequent asthma exacerbation, regardless of its precipitating trigger, can be attributed to NRP exposure.6 In urban areas in Southern California, NRP exposure may account for a substantial proportion of all air pollution-related exacerbations in children, which are commonly estimated on a population level only for regional pollutants.7,8,9

There has been little study of the costs of NRP-related health effects,10,11 which may be substantial.12 There are three categories of costs associated with these effects: direct costs are payments for healthcare; indirect costs reflect opportunity costs such as lost wages; and willingness to pay (WTP) to avoid the burden of asthma quantifies negative quality-of-life consequences.13 Population estimates of asthma-related costs have generally not quantified the day-to-day experience of asthma, because no robust studies had appropriately measured it.14,15,16

We developed a model of annual cost of childhood asthma that integrated novel methods from economics and epidemiology including WTP to avoid asthma morbidity17 and risk assessment incorporating asthma morbidity in children with NRP-attributable asthma.7 We evaluated the cost of pollution-related childhood asthma in Los Angeles county (LAC) in 2007 and the hypothetical cost per year of pollution-related childhood asthma under alternative levels of regional pollution and exposure to NRP.

LAC has a high prevalence of childhood asthma,18 dense traffic corridors, and high levels of regional air pollutants such as ozone (O3), nitrogen dioxide (NO2) and particulate matter. These regional levels are expected to continue to decline as a result of regulatory efforts.19 While a reduction in regional pollution should decrease the cost of asthma, the net impact when that reduction is combined with a change in the proportion of the population living near a major roadway is not obvious. Based on results of a previously published evaluation of pollution- related asthma exacerbations in LAC,7 we have now estimated (1) the childhood asthma-related costs attributable to regional and near-roadway pollution in 2007 and (2) the savings that might result from a 20% regional pollution reduction combined with a 20% increase or decrease in the proportion of families living in proximity to a major roadway relative to 2007 levels.7

Methods

Pollution-attributable asthma outcomes

The selection of pollutants, estimation of population exposure, concentration response functions (CRFs) and pollution-associated burden of asthma have been described previously.7 Briefly, we examined the effects of O3 and NO2 because each has a well-established causal relationship with asthma exacerbations.20,21 In Southern California, NO2 may be used as a proxy for general regional pollution (exclusive of O3) including particulate matter, elemental carbon, and nitric acid—all associated with respiratory health effects.22,23 O3 is relatively uncorrelated with other regional pollutants in the Los Angeles air basin.23,24 We avoided double counting pollution-attributable exacerbations by evaluating each pollutant separately.

The baseline exposure for all scenarios was the 2007 population-weighted proportion of LAC children living near a major roadway and the 2007 levels of regional pollution.7 A CRF for NRP was based on residence within 75m of a major roadway, a proxy for NRP exposure relevant for Southern California.5,9 Major roadways included freeways, highways or major arterial roads (functional road classes FRC01, FRC03 and FRC04 from the TeleAtlas MultiNet roads network7). In the first scenario, we estimated total asthma-associated costs of having 17.8% of the population living near major roadways by constructing a hypothetical in which this population’s NRP-exposure was reduced to background levels. We examined the costs imposed by the NO2 and O3 levels observed in LAC in 2007 as compared to their mean values in cleaner comparison cities in the Southern California Children’s Health Study that year (Scenarios 1A and 1B, respectively). The 2007 baseline measures of 24-hr NO2 across census tracts in LAC ranged from 6.2 to 31.4 ppb (population-weighted mean of 23.3 ppb). In Scenario 1A, we calculated the impact of a reduction in population-weighted NO2 exposure to 4 ppb across all census tracts. The 2007 baseline measures of 8-hr daily maximums for O3 across LAC ranged from 30.5 to 55.6 ppb (population-weighted mean of 39.3 ppb). In Scenario 1B, we reduced the population-weighted O3 exposure to 36.3 ppb. This first scenario generates the full asthma burden of the combined effects of NRP and regional pollution in LAC as compared to cleaner communities.

To illustrate the change in costs with respect to the two components of pollution-attributable asthma, we constructed hypothetical scenarios in which a decline in each regional pollutant was combined with either a 20% decrease (second scenario) or a 20% increase (third scenario) in the population percentage exposed to NRP. Since 17.8% of LAC children live near a major roadway, a change of 20% constitutes 3.56 percentage points. The hypothetical reductions in NO2 and O3 concentrations are plausible and based projections in the current air quality plan for Southern California.19 The health effects and their costs were estimated for a single year. When calculating outcomes in the hypothetical scenarios, we assumed that changes in the prevalence of asthma and resulting exacerbations were fully realized and instantaneous. These assumptions allowed us to compare costs across all of the scenarios and avoided the need for discounting.

For each scenario we used the near-roadway CRF to estimate the prevalence of asthma cases attributable to NRP in a given year.9 We estimated three types of exacerbations among children in LAC for one year:7 regional pollution-triggered outcomes among children with NRP-attributable asthma (Box 3, Figure 1), outcomes triggered by other factors among children with NRP-attributable asthma (Box 2, Figure 1), and regional pollution-triggered outcomes among children with asthma caused by factors other than NRP (“other-cause asthma”) (Box 6, Figure 1). Asthma exacerbation-related outcomes included: bronchitis episodes, hospital admissions, emergency room (ER) visits, doctor visits, and school absences for respiratory illness (for O3 only). Bronchitis, defined as a productive cough lasting three months or more, is a sensitive marker of NRP-attributable asthma exacerbations25 and is distinct from viral or bacterial bronchitis. We estimated the annual frequency of each outcome attributable to these regional pollutants using published CRFs for Southern California children, when available, or other appropriate CRFs when not. Supplement Tables 1 and 3 provide details on the CRFs and the baseline rates.

Figure 1.

Figure 1

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Outcomes Associated with Exacerbations and Routine Care Attributable to Pollution

Direct and indirect costs of an exacerbation

For each individual outcome we estimated the direct cost of goods and services and the indirect cost of caregivers’ lost wages. For the direct costs of healthcare, we used the amount charged rather than the amount paid, because amounts charged are not confounded by insurance status. All costs were expressed in 2010 dollars26 and sources are summarized in Supplement Table 2.

Direct costs of hospitalization and ER visits were calculated as the sum of facilities and physician charges.27,28 The direct cost of an office visit was estimated using the national mean charge for a physician visit.29 The direct cost of asthma inhalers (rescue and controller medications) was the average of the prices for each inhaler category weighted by the typical utilization of each category.30 The average price for each category of drug was the weighted mean of the name brand and generic prices.31,32

The indirect costs for office visits, ER visits and hospitalizations were the value of the caregiver's time spent traveling,33 waiting,34 and receiving care27,35,36 and were taken from secondary databases and peer-reviewed publications. We used one workday (eight hours) as the time for a school absence and valued time at the average wage rate.37 While this is the standard approach to valuing indirect costs, it overlooks the fact that caregivers of children with asthma sometimes leave the labor force to provide care.38 These caregivers face lower expected lifetime earnings even when they do return to the labor force.39

Direct and indirect costs of routine care

Children with asthma need more routine care than other children. These fixed costs of asthma (Box 1, Figure 1) include medication use and treatment for excess ear and sinus infections—an asthma-related comorbidity. The expected quantity for each outcome was estimated for children aged 0–17 in LAC using peer-reviewed literature and secondary databases (Supplement Table 2).30,40,41 Costs were calculated using the same approach as for exacerbations.

Direct and indirect costs of a bronchitis episode

Each bronchitis episode includes five potential costs: school absences,42 antibiotics prescriptions,43,44,45,46 office visits,47,48 ER visits,47,48 and inpatient hospital stays.47,48 We estimated the number of office visits, ER visits and hospital stays as the mean rate for children with asthma using the 2007 Medical Expenditure Panel Survey. These estimates are significantly lower than some reported rates.49

Willingness to pay

Bronchitis and asthma substantially impact quality of life.13,49,50 The value of this impact is quantified as the WTP to avoid this burden, using contingent valuation. A contingent valuation study offers participants a hypothetical health-related product, quotes prices, and inquires about WTP. Surveys must be designed to elicit values specific to desired health outcomes and to ensure valid responses.16 To meet these criteria we used the results of a contingent valuation study conducted in California among families with children with asthma.17

The WTP study17 was designed to estimate a WTP beyond the household’s current expenditures and included “debriefing” questions to ensure that the WTP was based on a desire to reduce the pain and suffering of asthma. Thus the estimate is specific to asthma and additive to the other costs. The quality-of-life burden of a single day of symptoms was calculated as the mean WTP divided by the mean number of symptom-days that would have been avoided using the hypothetical product.17 The hypothetical product offered a 50% reduction in days with asthma symptoms, so we doubled that estimate to determine the WTP to avoid a case of asthma.17

Using the WTP results,17 we calculated the quality-of-life value of symptom-days for bronchitis and ear and sinus infections. We multiplied the mean number of symptom-days in excess of those in children without asthma41 by the WTP to avoid a day with symptoms.17 The CRF was based on bronchitis lasting at least three months.25 We used a more conservative value of 35 symptom-days per episode, based on other studies examining the cost of cough lasting more than four weeks.50–52 The WTP estimate to assign costs to bronchitis episodes and ear and sinus infections17 was used because it is specific to children, consistent with our outcome definitions, and meets guidelines for validity.16 Our WTP estimates for these outcomes are more conservative than values extrapolated from existing literature by the Environmental Protection Agency.53

Results

We previously reported detailed estimates of the burden of pollution-attributable asthma in LAC that serve as the basis for our cost estimates.7 Briefly, we estimated that 27,100 cases of childhood asthma (4,900 to 51,200; 95% CI) are attributable to current NRP exposure, equivalent to 8% of the total current asthma burden in LAC. If proximity to roadways were reduced as in Scenario 2, there would be 5,900 (1,000 to 11,800; 95% CI) fewer cases of childhood asthma; increasing proximity as in Scenario 3 would have the exact opposite effect. Table 1 shows the change in the numbers of exacerbations under each scenario relative to the 2007 baseline. Among children with asthma, substantial proportions of the 2007 burden of bronchitis (57%), hospitalizations (20%), ER visits (11%), doctor visits (12%), and school absences (31%) were attributable to the combined effect of NRP exposure and regional pollution (Scenarios 1A and 1B in Table 1). The magnitude of bronchitis episodes attributable to pollution reflects the susceptibility of the population of children with asthma and the prevalence of asthma consequent to NRP-exposure. A reduction in regional pollution and in NRP exposure (Scenario 2) decreases all asthma outcomes; a reduction in regional pollution accompanied by an increase in NRP exposure (Scenario 3) increases all outcomes among those children with asthma due to NRP. Despite the decrease in regional pollution, the increase in cases of asthma due to NRP exposure leads to a net increase in ER visits, doctor visits and school absences (Scenario 3 in Table 1).

Table 1.

Decrease [increase in brackets] in the number of asthma outcomes under different exposure scenarios relative to baseline NRP exposure and regional pollution

Decrease [increase in brackets] in outcomes attributable
to regional air pollution among those with asthma due
to…		 Decrease [increase in brackets]
in outcomes due to other causes
among those with asthma due
to NRP		 Total decrease
[increase in brackets]
in outcomes
(1)+(2)+(3)
Near roadway
pollution (NRP)
(1)		 Other factors
(2)		 Both NRP and
other factors
(1)+(2)		 (3) (4)
Scenario 1A: Reduction in NRP-exposure and regional levels of NO2 to background levels
Bronchitis episodes 5600 59500 65100 5100 70200
  95% CI 660–12100 20500–85700 22500–92800 900–11700 31000–95700
Hospital admissions 30 340 375 235 610
  95% CI 5–65 265–420 295–450 50–450 410–840
Emergency room visits 35 370 405 1570 1970
  95% CI 5–85 65–670 75–725 320–2970 690–3400
Doctor visits 870 9200 10100 19800 29900
  95% CI 70–2140 1900–16500 2000–17900 4100–37700 12300–48900
Scenario 1B: Reduction in NRP-exposure and regional levels of O3 to background levels
Bronchitis episodes 1610 17200 18800 9100 27800
  95% CI 0–4050 530–32100 590–34900 1900–17600 9100–44300
Hospital admissions 1.9 20.7 22.6 270 290
  95% CI 0.3–4.2 10–31.7 10.9–34.3 50–510 80–530
Emergency room visits 11 121 133 1590 1730
  95% CI 2–23 75–167 84–181 330–3020 460–3160
Doctor visits 59 632 692 20600 21300
  95% CI 6–144 160–1111 175–1207 4200–39100 4800–39800
School absences 27900 302000 329900 86200 416100
  95% CI 449–70600 43800–562300 47700–612100 12000–168700 140200–681500
Scenario 2: Decrease in proportion of children living near major roadways and 20% reduction in regional pollution
Bronchitis episodes (NO2) 340 17600 17900 2000 19900
  95% CI 30–820 4800–29300 4900–29900 400–4100 6900–31700
Hospital admissions (NO2) 1 75 80 60 135
  95% CI 0–3 60–95 60–95 10–120 90–200
Emergency room visits (NO2) 2 80 80 350 430
  95% CI 0–4 15–145 15–150 70–700 140–790
Doctor visits (NO2) 40 2020 2060 4500 6600
  95% CI 0–100 400–3620 410–3700 860–9030 2530–11310
School absences (O3) 350 18710 19050 24400 43400
  95% CI 0–930 970–36510 980–37120 980–46800 14350–71760
Scenario 3: Increase in proportion of children living near major roadways and 20% reduction in regional pollution
Bronchitis episodes (NO2) [339] 17929 17589 [2009] 15580
  95% CI [33]–[824] 4875–29879 4769–29273 [382]–[4042] 2288–27758
Hospital admissions (NO2) [1] 79 77 [58] 19
  95% CI [3]-0 62–96 60–94 [11]–[116] [42]–70
Emergency room visits (NO2) [2] 81 80 [352] [272]
  95% CI [4]-0 15–148 14–145 [67]–[703] [630]-19
Doctor visits (NO2) [39] 2059 2020 [4519] [2499]
  95% CI [3]–[100] 411–3697 403–3629 [859]–[9037] [7305]-1552
School absences (O3) [349] 19194 18846 [24367] [5521]
  95% CI [930]-0 988–37354 968–36649 [968]–[46818] [34370]-23222
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Estimates are based on baseline outcomes, population and concentration-response functions reported in Perez et al. (2012). The baseline for each scenario is 2007 levels of NRP exposure and regional pollution. Scenario 1 is a 17.8 percentage point decrease in NRP exposure (to background levels of zero), decrease of 19.3 ppb of NO2 (Scenario 1A) and decrease of 3.03 ppb of O3 (Scenario 1B).

Scenario 2: Corresponds to a 3.56 percentage point decrease in NRP exposure, decrease of 3.9 ppb of NO2 and decrease of 0.61 ppb of O3 relative to the 2007 baseline.

Scenario 2: Corresponds to a 3.56 percentage point decrease in NRP exposure, decrease of 3.9 ppb of NO2 and decrease of 0.61 ppb of O3 relative to the 2007 baseline.

Values within brackets are an increase in the number of outcomes.

Table 2 shows the mean annual cost for a typical asthma case and the cost for a single bronchitis episode, broken down into direct cost [column (2)], indirect cost [column (3)] and WTP [column (4)]. The total annual cost of routine care (not including acute exacerbations) plus the quality-of-life cost as measured by WTP is approximately $3,000 for a single asthma case. The cost for a single episode of bronchitis is $1,500.

Table 2.

Costs of routine asthma care for a single case of asthma and a single bronchitis episode (in 2010 US $)

Annual cost for routine asthma case
Mean annual occurrence (1) Direct cost per occurrence (2) Indirect costs per occurrence* (3) WTP (4) Annual cost per asthma case (1)*[(2)+(3)+(4)]
Quality of life 1 N/A N/A 1549 1549
Medication
Inhaled corticosteroid 2.19 125 N/ A 273
Cromolyn 1.07 95 N/A 102
Albuterol 6.81 55 N/A 374
Comorbidities*
Doctor visits (non-urgent) 0.85 113 43 133
Mean cost of antibiotics 2.21 85 N/A 189
Urgent care visits 0.22 113 43 34
Hospital admissions 0.03 6,646 505 215
Days with symptoms 3.85 17 65
Total cost per year 2,934
Cost for a typical bronchitis episode
Mean occurrence per bronchitis episode (1) Direct cost per occurrence (2) Indirect cost per occurrence* (3) WTP per day (4) Mean cost per bronchitis episode (1)*(2+3+4)
Doctor visits 1.15 113 43 179
Emergency room visits 0.06 844 107 57
Hospital admissions 0.01 16625 747 174
School absences 2.00 N/A 220 440
Antibiotics 1.16 85 N/A 99
Days with symptoms 35 N/A N/A 17 595
Total cost per episode 1,544
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*

The mean times were: 46.6 minutes for round-trip travel for medical purpose,33 23 minutes waiting for office visit,34 24 minutes for receiving care,35 3.16 hours for visiting the ER,36 and 2.2 days for an asthma admission and 3.3 days for a bronchitis admission.27

The cost per year of asthma outcomes attributable to NRP and regional pollution for each scenario is the product of the quantity of each outcome due to pollution in that scenario (Table 1, column 4) and the cost of each outcome [Table 2, sum of columns (2)+(3)+(4)]. Table 3 shows the costs of the bronchitis episodes, hospital admissions, ER visits, doctor visits and school absences (O3 only) due to regional air pollution for children with asthma due to NRP [Column (1)] and children with other-cause asthma [Column (2)]. Column (3) shows the cost of those outcomes due to triggers other than regional pollution among children with asthma due to NRP. The sum of the cost of these outcomes for NO2 and exacerbation due to other triggers among those children with NRP-attributable asthma was $123 million [Table 3, Row (5), Column (5)]. A large portion ($108 million) is due to the reduction in bronchitis episodes brought on by pollution exposure. The cost of all outcomes among children with NRP-attributable asthma [the sum of the total row for NO2 in Column (1) of Table 3, $9m, and the total row for NO2 in Column (3), $15m], accounted for about 20% of the $123 million total.

Table 3.

Decrease [increase in brackets] in annual costs of exacerbations of childhood asthma under scenarios (in 1000s of 2010 US $)

Decrease [increase in brackets] in cost of exacerbations due to regional
air pollution among
children with asthma caused by…		 Decrease [increase in
brackets] in cost of
exacerbations due to
other causes among
children with asthma
due to NRP		 Decrease [increase
in brackets] in total
cost of exacerbations
NRP Other factors All factors
(1) (2) (1) + (2) (3) (1) + (2) + (3)
Scenario 1A: Reduction in NRP-exposure and regional levels of NO2 to background levels
Bronchitis episodes 8,646 91,868 100,514 7,874 108,389
  95% CI 1,019–18,636 31,652–132,321 34,740–143,283 1,390–18.065 47,864–147,761
Hospital admissions 398 4,516 4,980 3,121 8,101
  95% CI 66–863 3,519–55,778 3,918–5,976 664–5,976 5,445–11,156
Emergency room visits 33 352 385 1,493 1,873
  95% CI 5–81 62–637 71–689 304–2,824 656–3,233
Doctor visits 136 1,434 1,574 3,086 4,660
  95% CI 11–334 296–2,572 312–2,790 639–5,876 1,917–7,622
DECREASE IN COST IN SCENARIO 1A 9,213 98,170 107,453 15,574 123,023
  95% CI 1,101–19,914 35,529–191,308 39,041–152,738 2,997–32,741 55,882–169,772
Scenario 1B: Reduction in NRP-exposure and regional levels of O3 to background levels
Bronchitis episodes 2,486 26,510 29,012 14,050 42,923
  95% CI 0–6,258 823–49,522 908–53,898 2,934–27,174 14,050–68,399
Hospital admissions 25 275 300 3,586 3,851
  95% CI 4–56 133–421 145–465 644–6,773 1,062–7,039
Emergency room visits 10 115 126 1,512 1,645
  95% CI 2–22 71–159 80–172 314–2,872 437–3,005
Doctor visits 9 99 108 3,211 3,320
  95% CI 1–22 25–173 27–188 655–6,094 748–6,203
School absences 20,785 224,981 245,766 64,216 309,982
  95% CI 335–52,595 32,630–418,897 35,535–455,996 8,940–125,677 104,445–507,697
DECREASE IN COST IN SCENARIO 1B 23,315 251,980 275,312 86,575 361,721
  95% CI 342–58,953 33,682–469,172 36,695–510,719 13,487–168,590 120,742–592,343
Scenario 2: Decrease in proportion of children living near major roadways and 20% reduction in regional pollution
Bronchitis episodes (NO2) 525 27,174 27,638 3,088 30,726
  95% CI 46–1,266 7,411–45,239 7,566–46,166 618–6,330 10,654–48,945
Hospital admissions (NO2) 13 996 1,062 797 1,793
  95% CI 0–40 797–1,262 797–1,262 133–1,594 1,195–2,656
Emergency room visits (NO2) 2 76 76 333 409
  95% CI 0–4 14–138 14–143 67–666 133–751
Doctor visits (NO2) 6 315 321 701 1,029
  95% CI 0–16 62–564 64–577 134–1,407 394–1,763
School absences (O3) 261 13,938 14,192 18,177 32,332
  95% CI 0–693 723–27,199 730–27,653 730–34,865 10,690–53,459
DECREASE IN COST IN SCENARIO 2 807 42,499 43,289 23,096 66,289
  95% CI 46–2,019 9,007–74,402 9,171–75,801 1,682–44,862 23,066–107,574
Scenario 3: Increase in proportion of children living near major roadways and 20% reduction in regional pollution
Bronchitis episodes (NO2) [523] 27,682 27,157 [3,102] 24,056
  95% CI [51]–[1,272] 7,527–46,133 7,363–45,198 [590]–[6,241] 3,533–42,858
Hospital admissions (NO2) [13] 1,049 1,023 [770] 252
  95% CI [40]-0 823–1,275 797–1,248 [146]–[1,541] [558]–930
Emergency room visits (NO2) [2] 77 76 [335] [259]
  95% CI [4]-0 14–141 13–138 [64]–[668] [18]–[599]
Doctor visits (NO2) [6] 321 315 [704] [389]
  95% CI [16]-0 64–576 63–566 [134]–[1,409] [242]–[1,139]
School absences (O3) [260] 14,299 14,040 [18,153] [4,113]
  95% CI [693]-0 736–27,828 721–27,302 [721]–[34,878] [17,300]–[25,065]
DECREASE [INCREASE IN BRACKETS] IN COST IN SCENARIO 3 [804] 43,428 42,611 [23,064] 19,547
  95% CI [51]–[2,025] 9,164–75,953 8,957–74,452 [1,655]–[44,737] [24,368]–61,348
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The baseline was 2007 exposure to NRP and levels of NO2 and O3. Scenario 1 was17.8 percentage point decrease in NRP exposure (to background levels of 0). Scenario 1A was a decrease of 19.3 ppb of NO2, and Scenario 1B was a 3.03 ppb decrease of O3. Values may not sum due to y not sum due to rounding.

Scenario 2 was a 3.56 percentage point decrease in NRP exposure with decreases of 3.9 ppb of NO2 and 0.61 ppb of O3. Scenario 3 was a 3.56 percentage point increase in NRP exposure with decreases of 3.9 ppb of NO2 and 0.61 ppb of O3. Values within brackets are increases in cost. Values may not sum due to rounding.

The cost of outcomes due to O3 and exacerbations due to other triggers among children with NRP-related asthma totaled $362 million (Table 3, Scenario 1B). The differences between Scenario 1B and Scenario 1A are largely due to school absences due to O3. Across all O3 outcomes, 30% of the potential savings were due to reducing exacerbations among children with NRP-attributable asthma.

Scenarios 2 and 3 in Table 3 illustrate the combined effects of the 20% change in NRP exposure and the 20% reduction in regional pollution. We reported the estimated costs for the regional pollutant most responsible for each outcome: NO2 for all outcomes except school absences. Thus, if regional pollution were 20% lower than 2007 levels and the proportion of the population near roadways were reduced, there would be a decrease in the frequency of each outcome (from Table 1, Scenario 2), and a decrease in total costs (Table 3, Scenario 2) of approximately $66 million. If the decrease in regional pollution were accompanied by an increase in NRP exposure, then there would be an increase in each outcome that is triggered by regional air pollution or other factors among those with NRP-attributable asthma [from Table 1, Scenario 3, Columns (1) and (3) (in brackets to indicate an increase in disease burden)]. The total increase in costs would be $24 million [Table 3, Scenario 3, Columns (1)+(3)]. There would be a decrease in outcomes among those children with other-cause asthma [from Table 1, Scenario 3, Column (2)] and consequentially a decrease in costs of $43 million [Table 3, Scenario 3, Column (2)]. The net decrease in the total cost of all exacerbations in Scenario 3 would be $20 million. The exacerbations due to factors other than air pollution among children with NPR-attributable asthma [column (3)] account for most of the large difference between Scenarios 2 and 3 [a reduction of $23 million per year in Scenario 2 and an increase of almost that amount in Scenario 3].

Table 4 shows, for each scenario, the sum of the cost of exacerbations [column (1), which is the sum of columns (1)+(2)+(3) in Table 3] and of routine care for NRP-attributable asthma cases [column (2)]. Scenarios 1A and 1B in Table 4 reflect the total burden of NRP and regional pollution beyond that of cleaner comparison communities. A 100% reduction in major roadway proximity with a reduction in NO2 levels to those in clean communities (Scenario 1A) would save approximately $203 million annually. Elimination of NRP proximity and reduction of O3 to clean community levels (Scenario 1B) would save almost $441 million yearly. In Scenario 1A, 39% of the total cost of the current burden of NRP and regional NO2 is due to the cost of routine care for NRP-attributable asthma cases (the analogous figure for O3 is 18%). These NRP fixed costs have not been considered in previous regulatory risk assessments. The total cost savings achieved by reducing both regional pollution and proximity exposure (Scenario 2) are approximately $84 million; in comparison, increasing NRP exposure while reducing regional pollution provides a cost savings of only $2 million (Scenario 3). Thus, Scenario 3 suggests that the cost of the increased number of asthma cases due to NRP-attributable asthma eliminates almost all the savings of reducing regional pollution.

Table 4.

Decrease [increase in brackets] in the annual total costs of pollution-attributable asthma relative to baseline (in millions of 2010 US $)

Decrease in cost [increase in brackets] of
pollution-attributable exacerbations
(1)		 Decrease in cost [increase in
brackets] of routine care for
asthma due to NRP
(2)		 Decrease in total cost
[increase in brackets]

(1) + (2)
Scenario 1A
100% reduction in proportion of children living near major roadways AND reduction of NO2 to the background level of clean communities 123 80 203
  95% CI 56–170 14–150 70–320
Scenario 1B
100% reduction in proportion of children living near major roadways AND reduction of O3 to the background level of clean communities 362 80 441
  95% CI 121–592 14–150 135–743
Scenario 2
20% reduction in proportion of children living near major roadways AND 20% reduction in regional pollution 66 17 84
  95% CI 23–108 3–35 26–142
Scenario 3
20% increase in proportion of children living near major roadways AND 20% reduction in regional pollution 20 [17] 2
  95% CI [24]-61 [3]–[35] [27]-27
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Values within brackets are increases in costs. In scenarios 2 & 3, the pollution change is for NO2 for all outcomes except for school absences, for which we used O3. The cost of routine care is the cost for a case (Table 2) multiplied by the change in number of cases attributable to NRP exposure (decrease of 27,100 for Scenarios 1A and 1B, increase of 5,900 for Scenario 2, and decrease of 5,900 for Scenario 3). Values may not sum due to rounding.

The asthma-related impact of NRP is the sum of the cost of all exacerbations among children with NRP-attributable asthma [columns (1) and (3) from Table 3] and the cost of routine care for NRP-attributable cases [column (2) from Table 4]. Thus, if NRP exposure were eliminated, $104 and $189 million could be saved, respectively, by also reducing NO2 and O3 to levels in clean communities.

Discussion

The cost of air pollution-attributable childhood asthma is large—between $203 (for NO2) and $441 million (for O3) in 2007. For perspective, that was 6% and 13%, respectively, of the health department’s total expenditures on all health services for uninsured residents in LAC.54 A 20% decrease in regional pollution accompanied by a 20% decrease in the proportion of children living near major roads would reduce the cost of asthma by approximately $81 million more than if that decrease in regional pollution were accompanied by a 20% increase in the proportion of the population living near major roads. If policies such as replacing automobiles with electric vehicles or creating buffers between major roadways and children’s homes and schools are effective in eliminating cases of asthma attributable to traffic proximity exposure, the reduction in the total cost of the combined pollution-attributable burden would be 51% for NO2 and 43% for O3.

Expenditures to cover the direct costs of asthma represent a loss to society. In Los Angeles, 32% of children are covered by public insurance (Medi-Cal or Healthy Families);55 therefore, public funds pay for 32% of the direct pollution-attributable costs of asthma ($34 million a year for NO2). If this public expenditure were eliminated, that money could be used to extend Medi-Cal insurance to an additional 33,700 children each year (based on the cost of coverage and average healthcare expenditures56). Two doses of varicella vaccinations could be provided to an additional 135,218 children each year.57 If we invested the recovered funds in education, then full-time pre-school could be provided for an additional 2,358 children, producing a societal benefit of $49 to $132 million a year (based on returns to investment in early education58).

Our methodology relied on two key assumptions. First, we assumed that without exposure to NRP, the child would not have developed asthma. Some of these children might have nonetheless developed asthma due to other risk factors, which would render our costs an overestimation. Second, we assumed that the CRF of proximity would be the same under alternative hypothetical scenarios, but the effects of traffic-proximity as a proxy for NRP are likely to decrease if average vehicle emissions decrease in the future.

There are additional uncertainties in estimating costs. Based on the previously estimated burden of disease,7 we accounted for statistical uncertainty. Actual prices charged for healthcare vary over individuals; thus we used average estimates of charges. We also assumed that an NRP-attributable asthma case requires the same level of routine care and treatment for comorbidities as asthma due to other causes.

We assumed that outcomes associated with NO2 and O3 might affect the same individuals, and we did not sum the costs associated with each of these pollutants. In addition, some studies suggest that exposure to NO2 may potentiate the effect of O3,59 or that prior O3 exposure may exacerbate the effects of NRP in diesel exhaust.60 Therefore, these estimates would underestimate costs if the effects were additive. Last, we may have underestimated the total costs of pollution-related asthma because we omitted the costs associated with adult asthma.

Conclusions

By properly accounting for the effects of both NRP and regional pollution on asthma exacerbations, we identified large and previously unappreciated costs. Disaggregating the effects of regional pollution and NRP exposure helps clarify the health co-benefits and cost savings that could be achieved by reducing exposure to both regional and near-roadway pollution. Although our results are specific to LAC, they are relevant to other large metropolitan areas because of the large numbers of children living near major roadways across the U.S.1–2,61

Supplementary Material

Key messages.

  • The annual cost of asthma in Los Angeles County attributable to O3 is approximately $441 million and to NO2 approximately $202 million.

  • Routine care for children with asthma attributable to near-roadway pollution was 18% of the combined NRP and O3 cost and 39% of the combined NRP and NO2 cost.

  • NPR-attributable asthma accounted for 20% (NO2) to 30% (O3) of the cost of exacerbations due to pollution.

  • The cost of near-roadway pollution (NRP) accounted for 51% of total asthma-related cost due to NRP and regional NO2, and 43% of the total due to NRP and O3.

  • Cost of routine asthma care was almost $3,000 yearly for each child.

  • The actual public expenditures in 2007 on the asthma-related burden of pollution could have provided public insurance to 33,000 children, or 135,000 varicella vaccinations, or full-time preschool for 2,000 children.

Acknowledgments

Funding

This study was supported by the South Coast Air Quality Management District, a California state regulatory agency, with funds from a settlement with BP for violation of air quality regulations; NIEHS grants # R01 ES016535, P01ES011627, P30ES007048, P01ES009581, and 5R01ES014447; Environmental Protection Agency grants R826708, RD831861, R831845; and support from the Hastings Foundation.

Footnotes

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