Correlations between black carbon mass and size–resolved particle number concentrations in the Taipei urban area: A five–year long–term observation

This study investigates the correlation between Black Carbon (BC) mass and particle number concentrations in various particle size ranges in Taipei urban area. The concentrations of BC mass and particle numbers (ranging from 10–560 nm, N10–560) were measured continuously from 2006 to 2010. Long–term measurement results of this study demonstrated that BC mass concentrations in the spring, summer, autumn, and winter were 3.3 μg m−3, 3.2 μg m−3, 2.4 μg m−3, and 3.1 μg m−3, respectively. Additionally, the N10–560 concentrations in the spring, summer, autumn, and winter were 1.5 × 104 particles cm−3, 1.7 × 104 particles cm−3, 1.1 × 104 particles cm−3, and 1.4 × 104 particles cm−3, respectively. In the autumn, the lowest BC mass and particle number concentrations were mostly likely owing to the high wind speed condition that favored dispersion of particulate matter. Additionally, the highest particle number concentrations observed in the summer can be due to that the activities of the chemical nucleation reactions in the summer are more intense than those in other seasons. In this sampling site, the number fractions for N10–18, N18–32, N32–56, N56–100, N100–180, N180–320 and N320–560 were 4.39%, 15.38%, 26.31%, 27.35%, 16.89%, 7.17% and 2.51%, respectively. Hourly BC mass concentrations are significantly positively correlated with hourly N100–180 concentrations at the sampling site. In the summer, a clear increase in N10–560/BC is observed during the noontime period, coincident with maximum ambient temperature. Secondary particles through the photochemical nucleation heavily impact the size range of 56–100 nm, following by 100–180 nm and 32–56 nm in this study.