Continuous BC measurements were conducted with an Aethalometer at Tongyu from March to December 2008. The average BC concentration in PM2.5 at Tongyu was 2.52 ± 2.58 mgm−3, which is less than values of urban sites and larger than values of rural sites found in previous studies. Throughout the campaign, the lowest hourly BC value was 77.61 ng m−3
in autumn, close to the background level over the eastern Asia continent. The highest monthly average occurred in April (4.16 mgm−3) and the lowest in July (1.43 mgm−3). Hourly BC during four seasons generally showed a diurnal pattern similar to urban areas with two peaks at 22:00–00:00 UT and 8:00–10:00 UT.