A technique for determination of black carbon in cellulose filters

A technique has been developed to determine black carbon (BC) concentrations in aerosols collected on Whatman 41 (cellulose) filters using high-volume samplers. The cellulose substrate was dissolved in a 70% (w/v) solution of ZnCl2, and hydrosols were transferred to quartz filters, which were analyzed for BC using the thermal–optical method. The technique was applied to Whatman 41 and quartz filter blanks, filters with standards, and monthly composites made from daily samples collected during August 1993 and 1995 at Mayville and Whiteface Mountain, NY. The results show BC recoveries of 92.7±4.3% from cellulose filters. The blanks for the Whatman 41 filters were <1% of the BC observed on the filters. The BC concentrations at Mayville were determined to be 0.94±0.07 and 0.62±0.04 μg/m3 for August 1993 and 1995, respectively; the concentrations at Whiteface Mountain, NY for the same years were 0.39±0.03 and 0.40±0.02 μg/m3. Hence, the method developed here can be used to determine BC in Whatman 41 filters with an accuracy of about ±7%. The technique developed here will be used to determine BC concentration in filters collected daily from July 1978 to the present at Whiteface Mountain, and from July 1983 onwards at Mayville, NY. The data will be used to study long-term trends, seasonal variations, atmospheric transport, and source attributions for BC. The combined data for BC and (SO42−), may reveal the variations in fine particle mass over time.