Review of Adirondacks S02 Data 2008-2017
A review of 2008 - 2017 SO2 Data in the Adirondacks with Recommendations for Future Monitoring Options
Prepared by: Amanda C. Carpenter, Oliver V. Rattigan, Kevin L. Civerolo, and H. Dirk Felton
DEC collected hourly SO2 data at four locations in the Adirondacks as part of the monitoring network set up after the NYS Acid Deposition Control Act was signed in 1984. The three plus decades of SO2 data have shown consistent declines in concentration well correlated with reductions in emissions both within and upwind of New York State. One recent result of this decrease is that the continuous monitoring method is now inadequate in rural areas. Continuous SO2 analyzers were designed to produce data that can be compared to the higher concentrations relevant for the NAAQS. Features such as auto zeroing were not implemented for these instruments and EPA regulations do not allow post adjusting data to remove signal drift. Here we review data over the period 2008-2017.
NYSDEC Hourly Instruments
Thermo Electron 43A, 43B, 43C
- Reference Method ID: EQSA-0486-060
- Federal MDL: 2.0 ppb
- Used for hourly measurements from Jan 1, 2008 to March 31, 2016
Thermo Electron 43c-TLE/43i-TLE
- Reference Method ID: EQSA-0486-060
- Federal MDL: 0.2 ppb
- Max Acceptable Daily Drift: <0.2 ppb/day
- Used for hourly measurements from April 1, 2016 to most current
CASTNET Two Week Measurements
- 3-stage filter pack
- SO2 is captured on both the nylon and Whatman cellulose filters. The Whatman filters are impregnated with potassium carbonate. SO2 captured by the nylon and Whatman filters is combined to determine the total gaseous SO2 concentration.
Annual Means and Medians
Figure 4, above, shows the median concentration of hourly SO2 data collected from DEC monitors in the Adirondack Park study area. At many of the sites, the annual hourly medians are approaching or below the maximum acceptable daily drift of the instruments. Figure 4 has 0.2 ppb error bars.
Figures 5 and 6, above, show the box and whisker plots of the hourly SO2 data at two DEC sites. These plots show that the magnitude and frequency of outliers have been decreasing in both the NE and SW of the Adirondack Park during the study period.
Figures 7 and 8, above, show the daily averaged hourly data from DEC monitors (noted in orange), as well as the co-located CASTNET values during the same time period.
Figures 9 and 10, above, show the summer and winter diurnal patterns for the Whiteface Base site during 2008 and 2017. These charts show that SO2 concentrations have decreased and diurnal patterns have all but flattened out. The data suggests that there continues to be annual and seasonal variation.
Figure 11 Shows the percentage of hours per year where the hourly concentration of SO2 was equal to or below the maximum acceptable daily drift of the instrument. Note, 2017 data were truncated to remain consistent through the dataset.
Figures 12 and 13, above, show the change in the spatial gradient of the 99th percentile hourly SO2 concentration for the DEC instruments at both ends of the study period. The maps were made with the ArcMap Geostatistical Analysis Toolbox: Inverse Weighted Distance Tool. These maps show that 99th percentile values have both lowered and become more consistent over time throughout the study region.
Figure 14 shows that the annual average SO4 for CSN (WFM) and CASTNET sites are consistent across the region and have decreased by 60% since 2008.
Figure 15, above, shows the Total Sulfur values (SO2 + SO4) for three CASTNET sites: Nicks Lake, Whiteface Mountain and Underhill. This graph shows that while the magnitude of values have been decreasing, spatial variations between sites are still visible with the method.
As concentrations of SO2 have decreased, spatial variations have become less pronounced, diurnal patterns have flattened out and the hourly data have become less accurate. In 2017, all sites had greater than 50% of hours with SO2 concentrations equal to or less than the daily drift of the analyzer. This makes the determination of annual means problematic but still allows the data to be used to measure the impact of occasional spikes in concentration.
Hourly SO2 instrumentation at certain sites should be retained because of its intrinsic value (ability to detect short-term impacts, co-location verification for other methods, air quality modeling, trends analysis), but it is clear that other methods may be better suited for future deployment.
Seasonal and Annual variation of sulfur species need to be monitored and integrated sampling methods such as the CASTNET filter pack may be more appropriate for the Adirondacks.