Long term trends in Black Carbon Concentrations in the Northeastern United States

•Report trend in BC concentration at Mayville, NY from 1984 – 2010.•Mean BC at Mayville during 1984 was 600 ng m− 3 compared to 330 ng m− 3 in 2010.•Decreasing trend observed with a slope of -5.5 ng m− 3 per year.•32 months of Aethalometer BC measurements are also presented at Mayville NY.•Monthly means varied from 250 to 590 ng m− 3 with highest values during summer.

We report BC concentrations, ([BC]), measured using the thermal optical method, in monthly composites of daily particulate samples collected at rural Mayville, NY from 1984 to 2010. The monthly concentrations ranged from 10 to 900 ng m− 3, and showed decreasing trend with a slope of − 5.5 ng m− 3 per year, and a 32% decrease over the 27-year period. The monthly [BC] varied weakly with season but generally peaked in late summer. An aethalometer was also used to measure [BC], in real time, every 5 min from May 2008 to December, 2010. Measurements were made at 370 and 880 nm wave-lengths. Although both channels are calibrated as BC, fresh wood combustion emissions include polycyclic aromatic hydrocarbons that enhance the 370 nm channel signal. We utilize this to estimate that the wood burning contributed 18% of the BC on an annual basis, but accounted for ~ 30% in winter and ~ 8% during summer. BC concentration from local and transported sources was calculated based on aethalometer BC and HYSPLIT 4 air trajectories. The highest [BC] were associated with air masses that passed through the Ohio River Valley as well as through the Mid-Atlantic States. However, when integrated over time 68% of the BC transported to the site arrived from OH, KY, IN, IL, MI, WI, and southern Ontario.