Comparison of elemental and black carbon measurements during normal and heavy haze periods: implications for research

Studies specifically addressing the elemental carbon (EC)/black carbon (BC) relationship during the transition from clean-normal (CN) air quality to heavy haze (HH) are rare but have important health and climate implications. The present study, in which EC levels are measured using a thermal-optical method and BC levels are measured using an optical method (aethalometer), provides a preliminary insight into this issue. The average daily EC concentration was 3.08 ± 1.10 μg/m 3 during the CN stage but climbed to 11.77 ± 2.01 μg/m 3 during the HH stage. More importantly, the BC/EC ratio averaged 0.92 ± 0.14 during the CN state and increased to 1.88 ± 0.30 during the HH state. This significant increase in BC/EC ratio has been confirmed to result partially from an increase in the in situ light absorption efficiency ( σ ap ) due to an enhanced internal mixing of the EC with other species. However, the exact enhancement of σ ap was unavailable because our monitoring scheme could not acquire the in situ absorption ( b ap ) essential for σ ap calculation. This reveals a need to perform simultaneous measurement of EC and b ap over a time period that includes both the CN and HH stages. In addition, the sensitivity of EC to both anthropogenic emissions and HH conditions implies a need to systematically study how to include EC complex (EC concentration, OC/EC ratio, and σ ap ) as an indicator in air quality observations, in alert systems that assess air quality, and in the governance of emissions and human behaviors.