Measurements of PM2.5 mass and particle components over a 14–15 year period are used to explore trends at urban and rural locations across New York State. Such data are used to determine compliance with national ambient air quality standards (NAAQS), as well as track the effectiveness of reductions in source pollutant emissions. Since 2000 annual mean PM2.5 mass shows a downward trend with decreases of 4–7 µg m–3 in urban areas versus 3–4 µg m–3 for rural background sites. Much of this change can be attributed to particle sulfate (SO4) and nitrate (NO3) which showed annual decreases of 2–3 µg m–3 and 0.5–1.0 µg m–3, respectively. Determining accurate trends for the carbonaceous particle material is challenging due to the changes in the carbon sampling and analysis methods which impact the measurements. Analysis of the data indicate some decreases in particle elemental carbon (EC) but little change in the organic carbon fraction (OC). Significant improvements in air quality are observed since 2000, when New York City metropolitan area exceeded the 1997 annual PM2.5 standard of 15 µg m–3, to the present conditions where it meets the current standard of 12 µg m–3. Further improvements in air quality may benefit from controls on carbonaceous material which is currently the major component of PM2.5.