State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China.
State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China.
Environ Res. 2022 Jun;209:112791. doi: 10.1016/j.envres.2022.112791. Epub 2022 Jan 29.
Due to the lack of black carbon (BC) measurement data in some cases, elemental carbon (EC) is often used as a surrogate of BC, with a simple assumption that they are interchangeable. Such assumption will inevitably lead to uncertainties in radiative forcing estimation and health impact assessment. In order to quantitatively and systematically evaluate the relationship between BC and EC as well as factors responsible for their difference, 3-year collocated equivalent BC (eBC) and EC measurements with 1-h resolution were performed in Beijing, China continuously from 2016 to 2019. EBC concentration was measured by the multi-wavelength aethalometer (AE-33) based on optical analysis, while EC concentration was determined by semi-continuous OC/EC analyzer with thermal-optical method. The results showed that around 90% of eBC concentration was higher than that of EC, with average difference between eBC and EC as 1.21 μg m (accounting for 33% of average eBC in Beijing). EBC and EC concentrations exhibited strong correlation (r = 0.90) during the whole study period, but the slopes (or eBC/EC ratio) and correlation coefficients varied across seasons (spring: 1.67 and 0.94; summer: 0.91 and 0.65; fall: 1.15 and 0.88; winter: 1.09 and 0.91, respectively). Based on the information from shell/core ratios by Single Particle Soot Photometer (SP2), source apportionment results by positive matrix factorization model, and chemical composition of PM, the differences between eBC and EC concentrations were found to be primarily related to BC aging process and secondary components as evidenced by strong positive correlation with secondary species (e.g., secondary organic carbon and nitrate). This study provided seasonal specific conversion factors of eBC and EC in Beijing and helpful reference for other areas, which will contribute new knowledge of carbonaceous aerosol and reduce uncertainty in assessing future climate change and health studies of BC.
由于某些情况下缺乏黑碳 (BC) 测量数据，通常使用元素碳 (EC) 作为 BC 的替代物，假设它们是可互换的。这种假设不可避免地会导致辐射强迫估计和健康影响评估的不确定性。为了定量和系统地评估 BC 和 EC 之间的关系以及导致它们差异的因素，2016 年至 2019 年，在中国北京连续进行了为期 3 年、每小时分辨率的等效 BC(eBC) 和 EC 共置测量。eBC 浓度通过基于光学分析的多波长黑碳仪 (AE-33) 测量，而 EC 浓度则通过热光法的半连续 OC/EC 分析仪确定。结果表明，约 90%的 eBC 浓度高于 EC 浓度，eBC 和 EC 之间的平均差异为 1.21μg/m(占北京 eBC 平均值的 33%)。在整个研究期间，eBC 和 EC 浓度表现出很强的相关性(r=0.90)，但斜率(或 eBC/EC 比值)和相关系数在不同季节有所不同(春季：1.67 和 0.94；夏季：0.91 和 0.65；秋季：1.15 和 0.88；冬季：1.09 和 0.91)。基于单颗粒 soot 光度计 (SP2) 的壳核比信息、正矩阵因子模型的源分配结果以及 PM 的化学成分，发现 eBC 和 EC 浓度的差异主要与 BC 老化过程和二次成分有关，与二次物种(如二次有机碳和硝酸盐)呈强正相关。本研究提供了北京地区 eBC 和 EC 的季节性特定转换因子，为其他地区提供了有益的参考，有助于增加对碳质气溶胶的认识，减少评估未来气候变化和 BC 健康影响研究的不确定性。
