Description: This geospatial dataset contains annual concentrations measured at monitoring sites for air toxics covered in the 2014 National Air Toxics Assessment (NATA). These sites were not used directly to generate the NATA risk estimates because nationwide there are too few sites and monitored air toxics. For sites and pollutants with sufficient monitored values, measurements are summarized to indicate the distribution of measured concentrations. We provide concentrations for the NATA year, 2014, plus other years with enough monitoring data for us to compute annual concentration averages. Where available, we also provide measurements taken after 2014 to give you more recent information on pollutant concentrations at the monitor. In addition, we provide trends information so you can see how concentrations have changed over time.
In this dataset, users can explore for each site and monitored pollutant:
1) Descriptive statistics that show the distribution of the data for 2014 (where available) and the most recent year of monitoring data available. We only display sites with 2008 data or later. You can obtain the detailed daily (or hourly) measurement for any monitor from the air toxics archive (https://www3.epa.gov/ttnamti1/toxdat.html#data). 2) Monitored and modeled values used in the NATA model evaluation. Note that for modeled pollutant groups such as xylenes, the modeled value is not shown, as it reflects total xylenes and not the monitored individual components within the xylenes group (e.g., m/p-xylene and o-xylene). Also note that we did not use some sites for the model evaluation due to the impact of non-detected values. In these cases, both the modeled and monitored values will be missing. More information on model evaluation is provided in Section 3.7 of the NATA Technical Support Document (https://www.epa.gov/national-air-toxics-assessment/2014-nata-technical-support-document). 3) Trends plots that display the trends in annual concentrations over time. These are shown as box plots. Boxes display the 25th, 50th (median) and 75th percentile of the daily averages at the monitoring site. The whiskers show the 10th and 90th percentiles of the measurements. The dot is the annual mean. In these plots, the descriptive statistics are computed using a value of zero where the pollutant was not detected. Plots are not provided for sites with only 1 year of data or for which the 90th percentile concentration for all years is a non-detect.