Lobdell et al. Our analysis indirectly accounted for the concentrations in the city center, near the port 2030). We sorted the annual average concen- effects due to changes in key ethnic/racial areas, and near major roadways such as I-95, trations for 2001 in order to group the 318 demographic profile by using group or sex whereas PM2.5 concentrations in suburban study area locations (census block groups) for relevant hospitalization rates as part of the areas were much lower than in central parts of which we divided estimates into three groups health data and feasibility simulations. We the study area. Finally, PM2.5 concentrations according to average pollutant concentrations explored the influence of introducing an are projected to decrease over time, with the at baseline: low (locations in the lowest 25% additional explanatory variable in our health most pronounced decreases in areas with the of the distribution), medium (locations in the effects regressions to indirectly account for highest estimated concentrations in 2001. 2nd and 3rd quartiles), and high (locations both neighborhood effects and the missing Spatial patterns in ambient air quality in the highest quartile of the distribution). determinants of observed hospital admis- concentrations for NOx relates strongly to As expected, daily averages are more variable sions by computing average admissions either the sources of mobile emissions such as major than annual averages for both PM2.5 and within a 3- or 4-km radius around each cen- highways. NOx concentrations shown here NOx, which indicates the importance of tem- sus tract (similarly considered by Özkaynak depict strong spatial gradients because many poral variability in pollutant concentrations. and Thurston 1987). of the locations for which we estimated con- Downward trends in PM2.5 concentrations centrations (population-weighted centroids of were evident for areas with medium and high Results the 318 census block groups) are near major concentrations, but not for low-concentration Air quality modeling. We produced com- roadways. Thus, contrasts between those areas areas. Declines in NOx concentrations were bined CMAQ and AERMOD model results and suburban areas are very pronounced. evident over time for all three groups, but for the study area. Model estimates for NOx Finally, NOx concentrations are also projected the decrease was also much sharper in the and PM2.5 were consistent with measured Air to decrease considerably over time, particu- high-concentration areas. The models pre- Quality System (AQS) monitoring data for larly in locations close to roadways, because dicted large percentage decreases for NOx the area (Johnson et al. 2010). Figure 1 shows of the implementation of federal emission between 2001 and 2010 (61%) and with less maps of modeled PM2.5 and NOx concentra- standards for mobile source emissions. pronounced decreases from 2001 to 2020 tions for the baseline year (2001) and projec- Figure 2 shows distributions of annual and 2030 (overall decreases of 78% and 81%, tions for 2010, 2020, and 2030. PM2.5 maps and daily average modeled PM2.5 and NOx respectively). For PM2.5 the models predicted for all four time points show a wide range of concentrations for the baseline model year smaller percentage decreases from 2001 to concentrations in the study area, with high 2001 and projections (2010, 2020, and 2010 (8%), 2020 (9%), and 2030 (9%). PM2.5 PM2.5 NOx NOx 40 40 250 250 Annual averages 24-hr averages Annual averages 24-hr averages 3) 35 3) 35 Low group Low group ) Low group ) Low group 3m200 3m200 /m30 /m30 / / g g g g µ µ µ µ (s25 (s25 ( ( s150 s150 n n n n ito20 ito20 o o i i t t a a tra100 tra100 tr15 tr15 n n n n e e e e c10 c10 c c n n on50 on50 o o C 5 C 5 C C 0 0 0 0 2000 2010 2020 2030 2000 2010 2020 2030 2000 2010 2020 2030 2000 2010 2020 2030 40 40 250 250 Medium group Medium group Medium group Medium group 3) 35 3) 35 ) ) 3m200 3m200 /m30 /m30 / / g g g g ( µ 25 ( µ 25 µ µ ( ( s150 s150 s s n n n n io20 tio20 o o i i t t t a a tra100 tra100 tr15 tr15 n n n n e e e e c10 c10 c c n n on50 on50 o o C 5 C 5 C C 0 0 0 0 2000 2010 2020 2030 2000 2010 2020 2030 2000 2010 2020 2030 2000 2010 2020 2030 40 40 250 250 High group High group High group High group 3) 35 3) 35 ) ) 3m200 3m200 /m30 /m30 / / g g g g µ µ µ µ ( 25 ( 25 ( ( s150 s150 s s n n n n ito20 ito20 o o i i t t a a tra100 tra100 tr15 tr15 n n n n e e e e c10 c10 c c on50 on50 n n o o C 5 C 5 C C 0 0 0 0 2000 2010 2020 2030 2000 2010 2020 2030 2000 2010 2020 2030 2000 2010 2020 2030 Figure 2. Distributions of annual and daily average modeled PM2.5 and NOx concentrations for the baseline model year 2001 and projections for 2010, 2020, and 2030. The distributions for the census block groups are classified into three groups according to annual average PM2.5 and NOx concentration distributions in 2001: low, lowest 25%; medium, interquartile range; high, highest 25%. 490 119 | number 4 | April 2011 • Environmental Health Perspectives ovlume