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Table 1. The following table shows 3-year averages for the 98th percentile of PM2.5 concentrations. The first column lists the county; the second lists the average value for that county (rounded to the specifications of the standard). In Counties with more than one PM2.5 monitoring site, the value reported is the highest 3-year average among the inclusive sites. Averages for the counties marked with an asterisk are "unofficial estimates", because a sample size requirement ("data completeness") was not satisfied.
From 1999 until 2007, the national standard was set at 65 µg/m3. In 2007 the national standard was revised to 35 µg/m3. Catawba County exceeded the 2007 standard (but not the 1999 standard) in 2003-2005. All other counties are attaining the standards.
| County |
Average 98th Percentile |
| Alamance | 32 µg/m3 |
| Buncombe | 30 µg/m3 |
| Caswell | 30 µg/m3 |
| Catawba | 36 µg/m3 |
| Chatham | 26 µg/m3 |
| Cumberland | 31 µg/m3 |
| Davidson | 32 µg/m3 |
| Duplin | 27 µg/m3 |
| Durham | 32 µg/m3 |
| Forsyth | 32 µg/m3 |
| Gaston | 31 µg/m3 |
| Guilford | 31 µg/m3 |
| Haywood | 27 µg/m3 |
| Jackson | 25 µg/m3 |
| Lenoir | 26 µg/m3 |
| Martin | 24 µg/m3 |
| Mc Dowell | 31 µg/m3 |
| Mecklenburg | 32 µg/m3 |
| Mitchell | 28 µg/m3 |
| Montgomery | 27 µg/m3 |
| New Hanover* | 22 µg/m3 |
| Onslow | 24 µg/m3 |
| Orange | 29 µg/m3 |
| Pitt | 27 µg/m3 |
| Robeson | 30 µg/m3 |
| Swain | 27 µg/m3 |
| Wake | 32 µg/m3 |
| Watauga | 31 µg/m3 |
| Wayne | 28 µg/m3 |
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