1. Childhood Asthma and Exposure to Traffic and NO2
W. James Gauderman, Edward Avol, Fred Lurmann, Nino Kuenzli, Frank Gilliland, John Peters, and Rob McConnell
Epidemiology, Volume 16, Number 6, 2005
Presented by Nina Ewall

2. Introduction
NAAQS for NO2 is 53 ppb Nitrogen oxides are highly reactive gases mainly forming from vehicle emissions, off road equipment, power plants, fossil fuel combustion, and industrial processes Since 1980, NO2 concentrations have decreased 40% Average annual NO2 concentrations range between ppb
First some general information on traffic air pollution and nitrogen dioxide. National ambient air quality standard for no2 is 53 ppb. NO2 conc have decreased 40% from In the us average NO2 levels range between 10 to 20 ppb

3. NO2 levels are 30 – 100% higher near roadways (50 m)
Approximately 16% of U.S. housing are located within 300 ft of major roads
Nitrogen oxides (Nox ) includes both Nitrogen oxide (NO) and nitrogen dioxide (NO2)
Nox reacts with moisture, ammonia and other compounds to form small particles
Nox + VO + Sunlight, Heat = Ground Level Ozone (O3)
Short term exposure (30 min – 24 hours) to NO2 results in increased adverse respiratory effects and airway inflammation in various individuals
NO2 level may be between 30 to 100% higher near roadways. 16% of US housing is within 300 ft of major road. Nitrogen oxides include nitrogen oxide and nitrogen dioxide. Nitrogen oxides react with various compound to for small particles as well as ground level ozone. Short term exposure can have adverse respiratory effects.

4. Paper - Background
Irregular outcomes in studies examining an association between outdoor air pollution and asthma.
Why?
Research utilizes different traffic pollution exposure indicators: air monitoring outside home, centralized ambient air monitor, traffic volumes, residential distance to roads, modeling
There has been inconsistent results from studies that have examined the association between traffic air pollution exposure and asthma. Possible causes for these inconsistencies may be related to differences in traffic related indicators including: centralized ambient air monitors, monitoring near homes, traffic volumes, residential distance to roads, and models.

5. European studies have been conducted but variables such as home and street design and relative amounts of diesel to gasoline vehicles may vary
Studies of traffic exposure and asthma have been conducted in European cities but their applicability to the US cities have been questioned because of different urban blueprints.

6. Purpose
To determine whether changes in NO2 concentrations and indicators of exposure to traffic related pollution are associated with the prevalence of asthma (or indicators of asthma)
The purpose of the study is to investigate the relationship between indicators of traffic pollution including nitrogen dioxide monitoring outside participants homes and the prevalence of asthma (asthma outcomes).

7. Participants University of Southern California Children’s Health Study
1993 / Cohort 1 and 1996 /Cohort 2
4th graders (age - 10 years)
10 Southern California Communities (2 of 12 communities were excluded because of minor traffic)
Study requirements – subject stayed in same home since enrolling in the cohort studies
Randomly sampled 229 subjects of 890 children for NO2 monitoring
Participants are from the University of Southern California Children’s Health Study which is funded by Air Resources Board. The Children’s Health Study was initiated in 1992 and is a long term research program that examines the health effects of air pollution exposure in children living in Southern California. Children are generally more affected by air pollution than adults because they are developing, have a faster metabolism and spend more time outside. Subjects included 229 randomly selected 10 year-olds / 4th graders from two cohort studies (1993 and 1996). The children live in 10 southern California communities. Nitrogen dioxide monitors were placed outside the homes of the children.

8. Jerrett M, Shankardass K, Berhane K, Gauderman WJ, Kunzlie N, Avol E, Gilliland F, Lurmann F, Molitor J, Molitor J, Thomas DC, Peters J, and McConnell R, Traffic-Related Air Pollution and Asthma Onset in Children: A Prospective Cohort Study with Individual Exposure Measurement, October 2008, Environmental Health Perspectives, Volume116, Number10
Map of Communities

9. 10 Communities
Alpine, Atascadero, Lake Elsinore, Lancaster, Long Beach ,Mira Loma, Riverside, San Dimas Santa Maria and Upland
The ten communities are Alpine, Atascadero, Lake Elsinore, Lancaster, Long Beach, Mira Loma, Riverside, San Dimas, Santa Maria and Upland.

10. Nitrogen Dioxide Sampling
Palmes tube diffusion samplers placed outside each home for 2 week periods in summer (mid Aug.) and fall (mid Nov.) valid measurements (91%) for both seasons 10% subjects homes received duplicate samplers and travel field blanks 2 meters above ground (roofline eaves, signposts, rain gutters)
Nitrogen dioxide monitors were placed 2 meters above the ground outside the homes of participants for 2 week periods in summer (mid Aug) and Fall (mid November) during the year valid measurements were obtained for both seasons.

11. Traffic Pollution Exposure - Measurements
Distance from home to nearest freeway ( utilized ERSI ArcGIS Version 8.3 / both directions calculated) Average number of travelling vehicles within 150 meters from homes (freeways, arterials, major collector roads and minor roads, if possible) Model estimates of traffic related air pollution at residences, based on dispersion models (Distance to roadways, vehicle counts, vehicle emission rates, and meteorological conditions)
Traffic pollution exposure were assessed by several types of measurements: residential distance to the nearest freeways, average number of vehicles travelling within 150 meters of homes and model calculations of traffic air pollution from freeway and nonfreeway roads. The dispersion models included distance to roadways, vehicle counts, vehicle emission rates and metereological conditions.

12. Models – Source
Calculation of vehicle counts near homes (within 150 meters) was derived from daily traffic volumes
California Department of Transportation Highway Performance Monitoring System, 2000 or CALTRANS
Model calculations of traffic related pollution exposure
Based on CALINE4 line source air quality dispersion model
Input variables include roadway geometry, traffic volumes, meteorological conditions (wind speed, wind direction, atmospheric stability, mixing heights) and vehicle emission rates
Determination of vehicle counts came from daily traffic volumes supplied by CALTRANS or CA Dept. of Transpt Hwy Performance System.
Model Calculations utilized CALINE4 line source air quality dispersion model. Input variables included: roadway geometry, traffic volumes, meteorlogical conditions, vehicle emission rates
(5 year joint) Distributions of wind speeds and direction came from 1 surface monitoring station near or in each community.

13. 12 – 68% of NO2 levels are from local mobile source emissions.
Comparisons
Carbonmonoxide (CO) and fine particulate matter (PM) emissions also assessed to determine pollution exposure
NO2, CO and PM were found to be highly correlated (R>.90)
Investigators determined from separate regional modeling that 12 to 68% of average NO2 levels in the 10 communities are from mobile sources. Additionally, exposure criteria was also evaluated utilizing CO and PM emissions. Researchers found that NO2, CO, and PM were highly correlated with each other.

14. Asthma Questionnaire
“ Has a doctor every diagnosed your child as having asthma?” “yes”
Asthma related questions
Wheezed in past 12 months
Medication to control Asthma
Wheezed during exercised (12 months)
Asthma Risk Factors questions
Parental income, education, tobacco smoking, mildew, water damage, gas stove, pests and pets
Parents were unaware of the focus of the study at the time of completing the survey (self report bias)
Parents of the 4th graders were given a medical history questionnaire at the beginning of the study. Asthma was determined through doctor diagnosis. Included in the survey where questions regarding wheezing, asthma medication and wheezing during exercise. Additionally questions were asked about asthma risk factors including income, education, tobacco smoking in the home, mildew, water damage, gas stove, pest and pets

15. Statistical Analysis
A regression models were developed to obtain relationships for each traffic indicator and asthma prevalence
Natural log transformation (positively skewed)
Adjustments made for Hispanic ethnicity, cohort (1993 and 1996), race and sex
Separated models for 2 week (each season) and 4 weeks average
Odds Ratio (OR) were standardized to average interquartile range (IQR) for asthma and traffic indicators
Regression models were developed using natural log transformation because the traffic measurement variables were positively skewed. Adjustments in the models were made for Hispanic ethnicity, race, sex and cohorts (1993 or 1996). Investigators utilized separate models for the 2 week summer and fall seasons and the 4 week average. Odds ratio were adjusted to one interquartile range (25, 75 percentile) for traffic indicators and asthma.

16. Results
31 of the 208 study participants (15%) had doctor diagnosed asthma NO2 concentration range – 12.9 (Atascadero) to 51.5 ppb (San Dimas) Considerable variation of NO2 levels occurred from home to home within the communities. Usually variation increased in higher polluted communities ( exceptions were Mira Loma and Alpine)
31 participants (15%) were diagnosed with asthma. 4 week average NO2 levels ranged from 12.9 to 51.5 ppb in the 10 communities. Considerable variations of average NO2 levels occurred for the residences of each city.

17. Results Odds Ratios for 1 IQR (5.7ppb) of exposure (95%CI)
Outcome
Measured NO2
Distance to
Freeway
Model based Pollution From Freeways
Doctor diagnosed Asthma
1.83
( )
1.89
( )
2.22
( )
Strong associations were found between asthma prevalence and 3 measurements of traffic pollution exposure: NO2 monitoring outside the subjects home (OR = 1.83), distance to the nearest freeway (OR = 1.89), and model based pollution exposure to freeways (OR = 2.22). No relationships were observed with asthma and traffic volumes within 150 meters of homes or model based pollution estimates from smaller roads. Similar associations (odds ratios) were found with asthma outcomes of wheezing and asthma medication and the three measurements shown in the table.

18. Results
Why were no associations found between asthma and traffic volumes within 150 meters of homes or model based estimates for non freeway pollution ?
Number of vehicles on smaller roads is trivial (10s – 100s) compared to freeways (50,000 – 270,000)
Vehicle counts are less accurately estimated on smaller roads in comparison to freeways
Some Europe studies found association between asthma and traffic counts near residences
Urban geography and homes are closer to heavy traffic
Why were no associations found between asthma and traffic volumes within 150 meters of homes or model based estimates for non freeway pollution? Possible explanation could involve the number of vehicles on smaller roads is trivial (10s – 100s) compared to freeways (50,000 – 270,000) or vehicle counts are less accurately estimated on smaller roads in comparison to freeways. European studies did find a link to asthma and traffic volume near homes. This could be the result of different urban geography.

19. Table 1
Community (n = 208) NO2 (ppb) Community No. Asthma (%) Summer Winter Average† Alpine (AL) Atascadero (AT) Lake Elsinore (LE) Lancaster (LN) Long Beach (LB) Mira Loma (ML) Riverside (RV) San Dimas (SD) Santa Maria (SM) Upland (UP) *Parent report of doctor-diagnosed asthma in the child. †Mean in each community of NO2 concentrations measured at homes for 2 weeks each in summer and winter. Average is the 4 week arithmetic average of summer and winter measurements.
Nitrogen dioxide measurements and asthma cases for the 10 communities

20. Results: Figure 1 60 NO2 (ppb)
Measured NO2 outside the homes of study participants in the 10 communities.
4 week average of NO2 measured at homes of asthmatic (black) and non asthmatic children (white)

21. Base model, with additional adjustment for:
Association Between 4-Week Average NO2 at Homes and Asthma History Adjusted for Several Potential Confounders
Description OR* (95% CI)
Base model† (1.04–3.21)
Base model, with additional adjustment for:
Environmental tobacco smoke (1.09–3.43)
In utero exposure to maternal smoking (1.05–3.28)
Parental income (1.11–3.57)
Parental education (1.07–3.37)
Gas stove (1.06–3.30)
Mildew (1.01–3.23)
Water damage (1.03–3.21)
Cockroaches (1.04–3.21)
Pets (1.06–3.33)
*Odds ratio per increase of 1 interquartile range (5.7 ppb) in NO2.
†Base model includes adjustments for sex, race, Hispanic ethnicity, cohort, and community.
Table 2 – Relationships between NO2 measurements and asthma history includes confounders

22. Table 3 - Associations Between Exposure to Traffic at Home and Asthma History
Exposure Metric Odds Ratio per IQR
OR* (95% CI)
Distance to freeway (1.19–3.02)
Traffic volume within 150 meters (0.73–2.91)
Model-based pollution from:
Freeways (1.36–3.63)
Other roads (0.75–1.33)
Freeways and other roads (0.86–2.27)
*Odds ratio per change of 1 IQR. For distance to freeway, OR for the
25th percentile compared with the 75th percentile (ie, living closer compared
with farther from the freeway). For remaining traffic variables, OR for the
75th percentile compared with the 25th percentile. All models were adjusted for sex, race, Hispanic ethnicity, cohort, and community
Odds ratio for various traffic indicators: resident proximity to freeway, traffic volume within 150 meters and model based pollution exposure from freeways vs other roads

23. TABLE 4. Associations Between Measured NO2 and Asthma-Related Outcomes (n = 208)
Distance Model based pollution
Measured NO2 to Freeway From Freeway
Outcome No. OR* (95% CI) OR* (95% CI) OR* (95% CI)
Lifetime history of (1.04–3.22) (1.19–3.02) (1.36–3.63)
Recent wheeze† (1.07–2.77) (1.06–2.36) (1.12–2.58)
Recent wheeze
with exercise† (1.08–3.72) (1.50–4.38) (1.50–4.38)
Current asthma
medication use (1.20–4.01) (1.25–3.31) (1.18–3.12)
*Odds ratio per change of 1 IQR in exposure (see footnotes to Tables 2 and 4).
†Within the last 12 months.

24. Strengths:
Fairly strong associations were found between several indicators of exposure to traffic related air pollution in residences of S. California and asthma history (prevalence) and symptoms (wheezing)
Measuring NO2 levels or other relevant agents (PM, CO) is an important way to validate the use of traffic measurements as indicators of traffic exposure in a study population
Failure to validate traffic indicators may explain inconsistent results from other studies.
Strong associations were found between various indicators of traffic air pollution exposure in several communities near children's homes of S California. Measuring NO2 levels and other traffic related pollutants validates measurements of traffic exposure indicators in a study population.

25. Limitations
This is one study in one region and requires validation in other populations and communities.
It is unclear whether the prevalence of asthma in the study was related specifically to NO2 concentrations (5.7 ppb – low) or a combination of the other various traffic related pollutants associated with NO2
Concentration of fine particulate matter, black smoke (diesel exhaust)
This is one study in one region and requires validation in other populations and communities.
It is unclear whether the prevalence of asthma in the study was related specifically to NO2 concentrations (5.7 ppb – low) or a combination of the other various traffic related pollutants associated with NO2 such as concentration of fine particulate matter or black smoke (diesel exhaust).

26. Limitations
Determination of asthma in questionnaire maybe a reflection of access to healthcare and different diagnostic procedures among doctors .
Is there a more precise tool?
NO2 and traffic measurements were obtained after the onset of asthma and extrapolated to earlier ages
Freeways and major roads have been in the communities for many years
Determination of asthma in questionnaire maybe a reflection of access to healthcare and different diagnostic procedures among doctors but is there a more precise tool?
NO2 and traffic measurements were obtained after the onset of asthma and extrapolated to earlier ages but freeways and major roads have been in the communities for many years.