National Ambient Air Quality Standards
National Ambient Air Quality Standards (NAAQS) are ambient air quality standards set by the EPA to protect human health and the environment.  The two types of NAAQS are Primary Standards, which provide protection of public health, and Secondary Standards, which provide protection for public welfare (such as protection against decreased visibility, damage to plants and animals, and damage to property).  NAAQS have been established for six "criteria" pollutants: Carbon Monoxide (CO), Lead (Pb), Nitrogen Dioxide (NO2), Ozone (O3), Particulate Matter (PM2.5 and PM10), and Sulfur Dioxide (SO2).
In order to comply with the NAAQS, monitoring agencies must use EPA approved monitoring equipment and certified data to compute standard-related test statistics.  These statistics are calculated following the methods presented in the appendices of 40 CFR Part 50.  For concentration-based standards (as opposed to exceedance-based), the test statistic is also the design value, and can be directly compared to the applicable NAAQS.  If a design value is equal to or less than the NAAQS, or the test statistic meets the requirements set forth in 40 CFR Part 50, the area is in "attainment".  If the design value is greater than the NAAQS, or the test statistic fails to meet the requirements, the area is in "non-attainment".  When more than one monitor is located in the same area, the highest design value (or test statistic) will be used to determine the attainment status of that area.

South Dakota Ambient Air Quality for Criteria Pollutants
South Dakota operates an ambient air monitoring network designed, among other purposes, to determine compliance with the NAAQS.  Each year the state authors an annual monitoring network plan which provides great detail on the monitoring network and air quality data from the previous year.  These reports, along with additional helpful information, can be found on the state website: http://denr.sd.gov/des/aq/monitoring/state-mo.aspx.  South Dakota's ambient air quality for criteria pollutants (2010 through 2015), and how it compares to the primary standards, is discussed below.
The current primary carbon monoxide (CO) 1-hour and 8-hour NAAQS values are 35 ppm and 9 ppm respectively, and were promulgated in 1971.  Both of these values must not be exceeded more than once a year.  As shown in Table 1, two stations monitored for CO from 2010 through 2015.  Neither station recorded any values greater than 4% of the 1-hour NAAQS nor greater than 10% of the 8-hour NAAQS.  Regional and national CO trends for can be viewed at the EPA website www.epa.gov/air-trends/carbon-monoxide-trends.
The current primary annual and 1-hour NO2 NAAQS values are 53 ppb and 100 ppb respectively.  The annual NAAQS was promulgated in 1971 and the 1-hour NAAQS in 2010.  As shown in Table 2, five stations monitored ambient NO2 values throughout the state from 2010 through 2015.  All the stations had calculated design values that were well below both the primary annual and 1-hour NAAQS values.  Regional and national NO2 trends can be viewed at the EPA website www.epa.gov/air-trends/nitrogen-dioxide-trends.
The current Ozone NAAQS is 70 ppb and was promulgated on October 26[th], 2015.  As shown in Table 3, seven stations monitored ambient ozone values throughout the state from 2010 through 2015.    All stations had calculated design values that were under the primary 8-hour ozone NAAQS.  Regional and national ozone trends for can be viewed at the EPA website www.epa.gov/air-trends/ozone-trends.
Particulate matter with an aerodynamic diameter less than or equal to 2.5 microns is referred to as PM2.5.  The current PM2.5 1-year NAAQS is 12.0 ug/m[3], and the PM2.5 24-hour NAAQS is 35 ug/m[3].  As shown in Table 4, 13 sites monitored ambient PM2.5 values throughout the state from 2010 through 2015.  Eleven of the 13 stations had valid design values, and none of these 11 exceeded either NAAQS.  Regional and national PM2.5 trends can be viewed at the EPA website www.epa.gov/air-trends/particulate-matter-pm25-trends. 
Particulate matter with an aerodynamic diameter less than or equal to 10 microns is referred to as PM10.  The current 24-hour PM10 NAAQS is 150 ug/m[3], and was promulgated in 1987.  To determine compliance with the PM10 NAAQS, one must compute the average number of exceedances over three years, which is the standard-related test statistic for this pollutant.  For incomplete years, or for monitors collecting less frequently than on a daily schedule, the number of exceedances must be estimated, and is calculated as detailed in 40 CFR Part 50 Appendix K.  The standard is attained when the 3-year average estimated exceedance at each monitoring site is less than or equal to one.  As shown in Table 5, there were 13 sites monitoring ambient PM10 values throughout the state from 2013 through 2015.  Only one exceedance was recorded, and the exceedance was flagged by the state as an exceptional event.  As shown, the second maximum concentrations in 2015 were all under the NAAQS.  Design values are calculated using one of three methods detailed in the PM10 Development Guideline (EPA 1987) document.  Regional and national PM10 trends for can be viewed at the EPA website www.epa.gov/air-trends/particulate-matter-pm10-trends.
The current primary SO2 1-hour NAAQS is 75 ppb and was promulgated in 2010.  As shown in Table 6, six stations monitored ambient SO2 values throughout the state from 2010 through 2015.  Five of the six stations reported valid design values, and all were significantly lower than the 1-hour NAAQS.  Regional and national SO2 trends for can be viewed at the EPA website www.epa.gov/air-trends/sulfur-dioxide-trends.
Although there is a lead (Pb) NAAQS, monitoring is not required in South Dakota, nor was it performed from 2010 through 2015.  Regional and National Pb trends can be viewed at the EPA website www.epa.gov/air-trends/lead-trends.
