Abstract
Abstract. Mass concentrations of black carbon (BC) were determined in June 2006 at the top of Mount Tai (36.26° N, 117.11° E, 1534 m a.s.l.), located in the middle of Central East China, using four different instruments: a multi-angle absorption photometer (5012 MAAP, Thermo), a particle soot absorption photometer (PSAP, Radiance Research), an ECOC semi-continuous analyzer (Sunset Laboratory) and an Aethalometer (AE-21, Magee Scientific). High correlation coefficients (R2>0.88) were obtained between the measurements of the BC mass concentrations made using the different instruments. From the range of the slopes of the linear least-square fittings, we concluded that BC concentrations regionally-representative of the area were measured in a range with a maximum-to-minimum ratio of 1.5 (an exception was that the BC (PM2.5) concentrations derived from MAAP were ~2 times higher than the optical measurements (PM2.5) derived from the ECOC analyzer). While this range is significant, it is still sufficiently narrow to better constrain the large and highly uncertain emission rate of BC from Central East China. In detail, two optical instruments (the MAAP and the PSAP equipped with a heated inlet 400°C) tended to give higher concentrations than the thermal EC concentrations observed by the ECOC analyzer. The ratios of optical BC to thermal EC showed a positive correlation with the OC/EC ratio reported by the ECOC analyzer, suggesting two explanations. One is that the optical instruments overestimated BC concentrations in spite of careful cancellation of the scattering effect in the MAAP instrument and the expected evaporation of volatile species by heating the inlet of the PSAP instrument. The other is that the determined split points between OC and EC were too late when a large amount of OC underwent charring during the analysis, resulting in an underestimation of EC by the ECOC analyzer. High ratios of optical BC to thermal EC were recorded when the NOx/NOy ratio was low, implying the coating of the particles became thicker in an aged air mass and thus resulted in the optical instruments overestimating BC concentrations because of the lensing effect.
Highlights
Black carbon (BC) aerosol particles are an important component of the atmosphere contributing to global warming
The high concentrations likely stem from significant open biomass burning of crop residues over the North China Plain as discussed elsewhere (Li et al, 2008; Akimoto et al, 2008). It should be noted in the following discussion that the high concentration episodes occurred during Period 1, when the National Institute for Occupational Safety and Health (NIOSH) program was employed for the ECOC analyzer
In a more detailed analysis, it is inferred that the elemental carbon (EC) concentrations determined with the Interagency Monitoring of Protected Visual Environments (IMPROVE)∗ temperature rise program for the ECOC analyzer were higher than those with the NIOSH program by 31% and showed slightly better agreement with the MAAP BC values
Summary
Black carbon (BC) aerosol particles are an important component of the atmosphere contributing to global warming. There has been much discussion about the selection of the temperature program and the mass absorption/attenuation coefficient assumed to calculate BC concentrations from the optical measurements, solid and systematic conclusions have not yet been reached. In this situation, one approach for the better quantification of BC concentrations would be to make measurements using several instruments and examine the differences. A PM1 cyclone (URG-2000-30EHB) was used for the PSAP instrument before 20 June, 04:00 CST, but it was replaced by a PM2.5 cyclone (URG-2000-30EH) on 20 June, 05:00 CST For both heated and unheated measurements, a single mass absorption coefficient 10 m2 g−1 at 565 nm was employed to convert the light attenuation to the BC mass concentration as recommended by the manufacturer. We first use the cross sections recommended by the manufacturers for simplicity and discuss systematic differences in the BC concentrations derived from the instruments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
