PNAS:炭黑在被污染的城市中心的效应
美国德克萨斯A&M大学一项研究提出，减少城市中心的炭黑污染可能改善空气质量并且防止气候变暖。燃烧化石燃料和生物质会向大气层释放出称为炭黑的精细的碳颗粒。尽管研究已经表明了炭黑能吸收太阳能并加热周围的空气，准确确定这种致暖的量级仍然具有挑战性。Renyi Zhang及其同事设计了一个实验腔，用于观测炭黑颗粒如何随着时间推移变化，并且进行了模拟中国北京和美国德克萨斯休斯敦的周围环境条件的实验。这组作者识别出了两个不同的黑炭转变阶段：最开始是形状变为球形，之后是生长成密度更大的颗粒，具有大的吸收属性。这组作者报告说，在这两个城市，这种转变以不同的速度发生，在北京仅需要2到4小时，相比之下在休斯敦需要大约9到18个小时。这组作者说，北京环境中的高水平的污染物迅速包覆了炭黑颗粒并加速生长，这个推进污染的反馈通过让大气边界层变暖并稳定化，加剧了严重霾的暴发。
原文链接：
Markedly enhanced absorption and direct rADIative forcing of black carbon under polluted urban environments
原文摘要：
Black carbon (BC) exerts profound impacts on air quality and climate because of its high absorption cross-section over a broad range of electromagnetic spectra, but the current results on absorption enhancement of BC particles during atmospheric aging remain conflicting. Here, we quantified the aging and variation in the optical properties of BC particles under ambient conditions in Beijing, China, and Houston, United States, using a novel environmental chamber approach. BC aging exhibits two distinct stages, i.e., initial transformation from a fractal to spherical morphology with little absorption variation and subsequent growth of fully compact particles with a large absorption enhancement. The timescales to achieve complete morphology modification and an absorption amplification factor of 2.4 for BC particles are estimated to be 2.3 h and 4.6 h, respectively, in Beijing, compared with 9 h and 18 h, respectively, in Houston. Our findings indicate that BC under polluted urban environments could play an essential role in pollution development and contribute importantly to large positive radiative forcing. The variation in direct radiative forcing is dependent on the rate and timescale of BC aging, with a clear distinction between urban cities in developed and developing countries, i.e., a higher climatic impact in more polluted environments. We suggest that mediation in BC emissions achieves a cobenefit in simultaneously controlling air pollution and protecting climate, especially for developing countries.
作者：Jianfei Peng
