Control days were chosen within the same month of the same year to control for season, and matched on either sulfur dioxide (SO2; within 1 ppb), nitrogen dioxide (within 1 ppb), maximum ozone (within 2 ppb), or carbon monoxide (within 0.03 ppm).
Pollutant included 1-hr maximum carbon monoxide (CO) in ppm, 1-hr maximum nitrogen dioxide (NO2) and nitrous oxides (NO x) in ppb, 8-hr maximum ozone (O3) in ppb, 1-hr maximum sulfur dioxide (SO2) in ppb, and five 24-hr average PM2.5 components in μg/m: elemental carbon (EC), organic carbon (OC), nitrate (NO3), ammonium (NH4), and sulfate (SO4).
Pollutants included in the analysis included measures for 1-hr maximum carbon monoxide (CO) in ppm, 1-hr maximum nitrogen dioxide (NO2) and nitrous oxides (NO x) in ppb, 8-hr maximum ozone (O3) in ppb, 1-hr maximum sulfur dioxide (SO2) in ppb, and five 24-hr average PM2.5 components in μg/m: elemental carbon (EC), organic carbon (OC), nitrate (NO3), ammonium (NH4), and sulfate (SO4).
The 1-hr maximum ozone was 100.13 ppb.
Mean (± SD) ambient 1-hour maximum ozone concentration was 71 (18) ppb.
Across all 91 counties, the mean observed daily 8-hour maximum ozone concentration was 46 ppb and the mean warm-month daily maximum temperature was 74°F.
The frequency of asthma ED visits was 33% higher (95% CI, 10-56%) when the daily 1-hr maximum ozone concentration exceeded 75 ppb (the 95th percentile).
For both methods, we assume a constant background 8-hr daily maximum ozone level of 40 ppb, representing the amount of ozone (for this averaging period) that is not attributable to U.S. anthropogenic sources.
Relative to the 2030 reference scenario, implementing the methane measures (Table 1) would decrease seasonal (6-month) average 1-hr daily maximum ozone concentrations by 3 4 ppb (Table 2 and Figure 3).
By 2100, much of the Northern Hemisphere was projected to have annual mean maximum ozone levels of 60 ppb, as were most of the populated areas of the Southern Hemisphere (Anderson et al. 2001).
