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. 2020 Jun 1;128(6):067003. doi: 10.1289/EHP6174

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Figure 1 is a flow chart with six steps. Step 1. SAPALDIA 1 1991; n equals 9,551. Step 2. SAPALDIA 2 2002; n equals 8,047. Step 3. SAPALDIA 3 2010; n equals 6,088. Step 4. SAPALDIA 2 2002; n equals 8,047 is divided into two parts ALEC and EXPOsOMICS. ALEC leads to 987 representative sample selected for D N A methylation assessment; 983 participants with methylation data overlapping C p Gs passing quality control; and 972 participants with complete data on transportation noise, air pollution, and relevant covariates. EXPOsOMICS leads to 201 nonsmoking asthma controls selected for DNA methylation assessment; 198 participants with methylation data in overlapping C p Gs passing quality control; and 198 participants with complete data on transportation noise, air pollution, and relevant covariates. ALEC and EXPOsOMICS lead to 1,170 participants included in the analysis. SAPALDIA 3 2010; n equals 6,088 is divided into two parts ALEC and EXPOsOMICS. ALEC leads to 987 participants (same SAPALDIA 2 participants) selected for DNA methylation assessment; 983 participants with methylation data in overlapping C p Gs passing quality control; and 970 participants with complete data on transportation noise, air pollution, and relevant covariates. EXPOsOMICS leads to 405 nonsmoking participants [201 non-asthma controls (same SAPALDIA 2 participants) and 204 asthma cases] selected for DNA methylation assessment; 402 participants (198 asthma controls and 204 asthma cases) with methylation data overlapping CpGs passing quality control; and 402 participants (198 asthma controls and 204 asthma cases) with complete data on transportation noise, air pollution, and relevant covariates. ALEC and EXPOsOMICS lead to 1,372 participants included in the analyses. The final outcome is 1,389 participants contributing 2,542 observations to final analyses: 985 ALEC participants contributing 1,942 observations and 404 EXPOsOMICS participants contributing 600 observations. — Selection of participants included in the present study. SAPALDIA: Swiss cohort study on air pollution and lung and heart diseases in adults. ALEC: Aging lungs in European cohorts. ALEC and EXPOsOMICS are European cohort consortia in which SAPALDIA participates. DNA methylation was measured using Illumina Infinium 450K BeadChip and processed in the same manner across the ALEC and EXPOsOMICS samples to derive the residuals of the beta values (corrected for technical bias) of overlapping 430,477 CpGs, which were subsequently applied to the present epigenome-wide association study.