Supplementary Material Contents Figure S1. Study areas consisted of 9 cities and wards (Chiba City, Itabashi Ward, Suginami Ward, Setagaya Ward, Kawasaki City, Yokohama City, Nagoya City, Osaka City, and Kobe City). Figure S2. Correlation between outdoor concentrations and personal exposure levels (n=428) Table S1 online. Outdoor concentrations and personal exposure levels of NOx and EC in mean ± SD (n=428). Table S2 online. Correlation coefficients between air pollutants in baseline survey (n=63,266). Table S3. Descriptive data for two-stage nested case-control study (n=428). Table S4. Additional analyses of associations between incidence of asthma from 1.5 to 3 years and outdoor NOx or EC concentrations using a logistic model, adjusted for potential confounding variables (n=39,539). The definition of confounding variables in Table 2 and 4 The definition of confounding variables in Table 3 Appendix A: Personal exposure levels of NOx and EC for each subject Appendix B: Organization of the Japan national Study on Respiratory Disease and Automobile Exhaust (SORA) 1 Figure S1. Study areas consisted of 9 cities and wards (Chiba City, Itabashi Ward, Suginami Ward, Setagaya Ward, Kawasaki City, Yokohama City, Nagoya City, Osaka City, and Kobe City). 2 120 6 y = 0.909x + 16.6 100 r² = 0.888 5 y = 0.590x + 0.327 r² = 0.928 80 4 ) 3 60 3 (μg/m 40 2 20 1 of EC level exposure Personal 0 0 0 20 40 60 80 100 120 (ppb) of NOx level exposure Personal 0 1 2 3 4 5 6 Outdoor concentration of NOx (ppb) Outdoor concentration of EC (μg/m3) Figure S2. Correlation between outdoor concentrations and personal exposure levels (n=428). 3 Table S1. Outdoor concentrations and personal exposure levels of NOx and EC in mean ± SD (n=428). Outdoor Concentration Personal exposure level mean ± SD mean ± SD NOx (ppb) 37.7 ± 7.8 55.3 ± 10.4 EC (μg/m3) 2.85 ± 0.45 2.13 ± 0.35 Abbreviations: NOx, nitrogen oxides; EC, elemental carbon. 4 Table S2. Correlation coefficients between air pollutants in baseline survey (n=63,266). EC NOx NO2 SPM Ox EC - 0.88 0.40 0.31 0.27 NOx - - 0.49 0.05 0.21 NO2 - - - 0.20 0.37 SPM - - - - 0.43 Ox - - - - - Abbreviations: EC, elemental carbon; NOx, nitrogen oxides; NO2, nitrogen dioxide; SPM, suspended particulate matter; Ox, photochemical oxidants. 5 Table S3. Descriptive data for two-stage nested case-control study (n=428). Case Control High-exposure Low-exposure High-exposure Low-exposure N % N % N % N % Subjects 40 100.0 138 100.0 126 100.0 124 100.0 Gender Boys 24 60.0 88 63.8 77 61.1 82 66.1 Girls 16 40.0 50 36.2 49 38.9 42 33.9 Year of birth 2005 22 55.0 76 55.1 72 57.1 68 54.8 2006 18 45.0 62 44.9 54 42.9 56 45.2 Kaup index 18 or more 6 15.8 13 9.6 9 7.4 5 4.1 Less than 18 32 84.2 122 90.4 113 92.6 117 95.9 History of attendance in nursery school/kindergarten Yes 32 80.0 105 76.1 90 71.4 91 73.4 No 8 20.0 33 23.9 36 28.6 33 26.6 Past history of wheezing Yes 23 57.5 77 55.8 31 24.6 29 23.4 No 17 42.5 61 44.2 95 75.4 95 76.6 Past history of bronchitis or pneumonia Yes 22 55.0 88 64.2 28 22.2 31 25.0 No 18 45.0 49 35.8 98 77.8 93 75.0 Past history of bronchiolitis Yes 7 17.5 25 18.1 6 4.8 8 6.5 No 33 82.5 113 81.9 120 95.2 116 93.5 Past history of atopic dermatitis Yes 9 22.5 39 28.3 15 11.9 7 5.6 No 31 77.5 99 71.7 111 88.1 117 94.4 Past history of allergic rhinitis Yes 9 22.5 25 18.1 15 11.9 8 6.5 No 31 77.5 113 81.9 111 88.1 116 93.5 Past history of food allergy 20.6 Yes 10 25.0 49 35.5 12 9.5 18 14.5 No 30 75.0 89 64.5 114 90.5 106 85.5 Past history of five or more episodes of high fever Yes 31 77.5 111 80.4 75 59.5 70 56.5 No 9 22.5 27 19.6 51 40.5 54 43.5 Birth order 1st 18 45.0 70 50.7 59 46.8 68 54.8 2nd and over 22 55.0 68 49.3 67 53.2 56 45.2 Parent with asthma Yes 8 20.0 64 46.4 24 19.0 28 22.6 No 32 80.0 74 53.6 102 81.0 96 77.4 Structure of house Wooden house 11 27.5 39 28.3 39 31.0 38 30.6 Steel-frame building 29 72.5 99 71.7 87 69.0 86 69.4 Heating system Without ventilation 23 57.5 56 40.6 47 37.3 64 51.6 With ventilation 17 42.5 82 59.4 79 62.7 60 48.4 Keeping pets (fowl, mammals) Yes 10 25.0 31 22.5 19 15.1 24 19.4 No 30 75.0 107 77.5 107 84.9 100 80.6 6 Familial smoking habits Yes 11 27.5 40 29.0 25 19.8 31 25.0 No 29 72.5 98 71.0 101 80.2 93 75.0 Feeding method during the first 3 months of life Brest milk only 14 35.0 40 29.0 33 26.2 27 21.8 Others 26 65.0 98 71.0 93 73.8 97 78.2 Influenza vaccine Yes 22 55.0 98 71.5 76 60.8 83 66.9 No 18 45.0 39 28.5 49 39.2 41 33.1 Specific IgE tests Positive 16 84.2 61 82.4 30 56.6 18 51.4 Negative 3 15.8 13 17.6 23 43.4 17 48.6 Bedding mite allergen test Positive 9 37.5 43 43.4 23 30.3 21 24.1 Negative 15 62.5 56 56.6 53 69.7 66 75.9 7 Table S4. Additional analyses of associations between incidence of asthma from 1.5 to 3 years and outdoor NOx or EC concentrationsa using a logistic model, adjusted for potential confounding variablesb (n=39,539). NOx EC Odds Ratio (95% CI) Odds Ratio (95% CI) Level 5 0.71 (0.48, 1.05) 0.70 (0.47, 1.03) Level 4 0.85 (0.66, 1.09) 0.89 (0.68, 1.17) Level 3 0.80 (0.64, 1.09) 0.84 (0.65, 1.09) Level 2 0.80 (0.64, 0.99) 0.92 (0.72, 1.16) Level 1 1.00 1.00 Abbreviations: NOx, nitrogen oxides; EC, elemental carbon; CI, confidence interval. a Outdoor NOx concentrations of level 1 to 5 are 13.9-32.5, 32.6-37.1, 37.2-42.0, 42.1-50.8, and 50.9-136.8 ppb, respectively. Outdoor EC concentrations of level 1 to 5 are 1.3-2.4, 2.5-2.7, 2.8-3.0, 3.1-3.5, and 3.6-7.5 μg/m3, respectively. b Potential confounding variables include gender, districts, birth season, years of residence, feeding method during the first three months of life, familial smoking habits, structure of house, heating system, keeping pets (cats, birds, dogs, hamsters, others), background concentration of air pollutants, past history of disease before the age of 1.5 years, such as bronchitis/pneumonia, empyema, and allergic disease; and parental history of allergic diseases, such as asthma, atopic dermatitis, and pollinosis. 8 The definition of confounding variables in Tables 2 and 4: (1) Birth season: Categorization of Children’s birth season, December to February, March to May, June to July or September to November; (2) Years of residence: Categorization of how many years in which the child lived at the current residence, “below 1 year”, “over 1 year” or “live in the same residence since birth”; (3) Feeding method during the first three months of life: Categorized into breast milk, bottle feeding or both; (4) Familial smoking habits: Categorized into mother, others, or none who smoked in the same house with the child; (5) Structure of house: Categorized into wooden house or steel-frame/concrete building; (6) Heating system: A ventilation system was equipped with heating devises; (7) Keeping pets: Keeping cats, birds, dogs, hamsters, or other pets in the house; (8) Background concentration of air pollutants: Suspended particulate matter (SPM) and photochemical oxidants (Ox) for NOx model, nitrogen dioxides (NO2) and Ox for EC model; (9) Past history of bronchitis/pneumonia: The child received treatment for bronchitis/pneumonia before the age of 1.5 years; (10) Past history of empyema: The child received treatment for empyema before the age of 1.5 years; (11) Past history of allergic disease: The child received treatment for allergic disease before the age of 1.5 years ; (12) Parental history of asthma: Either mother or father has received treatment for asthma. (13) Parental history of atopic dermatitis: Either mother or father has received treatment for dermatitis; (14) Parental history of pollinosis: Either mother or father has received treatment for pollinosis.