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首页> 外文期刊>Atmospheric environment >Measurements of the impact of atmospheric aging on physical and optical properties of ambient black carbon particles in Los Angeles
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Measurements of the impact of atmospheric aging on physical and optical properties of ambient black carbon particles in Los Angeles

机译：大气老化对洛杉矶周围环境黑碳颗粒的物理和光学性质的影响的测量

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Understanding how physical and optical properties of atmospheric black carbon (BC) particles vary in time and space is critical for reducing uncertainty in climate forcing estimates from ambient BC. In this study, ambient BC was measured in Rubidoux, California, approximately 90 km (55 miles) downwind of downtown Los Angeles. Collocated NOx and NOy measurements were used to estimate the photochemical age of the sampled air. Sampling was conducted throughout entire days between February 3, 2015 and March 12, 2015 to capture diurnal and daily variations in ambient BC. Both ambient and thermally-denuded air was sampled in 15-min cycles to compare the physical and optical, properties of coated versus uncoated BC particles. Physical properties of individual BC particles including mass and coating thickness were measured using a Single-Particle Soot Photometer (SP2), and BC optical properties were measured using a Photoacoustic Extinctiometer (PAX) at 870 nm. The mean BC mass concentration (+/- standard deviation) for the campaign was 0.12 +/- 0.08 mu g m(-3). BC mass concentrations were higher on weekdays than weekends, though only differences between 11:00 and 17:00 h were statistically distinguishable. The fraction of total BC particles that were thickly-coated (f) was found to be relatively low, with a mean of 0.05 +/- 0.02 over the campaign. Values for f peaked in the afternoon when photochemical pollutant concentrations are also generally at a maximum. Further, fat 15:00-16:00 h was found to be statistically higher on weekends than weekdays, potentially due to a higher relative amount of ambient SOA to BC on weekends versus weekdays, which would enhance SOA coating of primary BC particles as they age during transport from the western Los Angeles basin to our sampling site on weekends. Differences at other hours during the photochemically active period of the day (10:00 14:00 h) were not statistically different although the weekend values were systematically higher. Comparing f with the photochemical age (PCA) of sampled air showed increases in f as PCA increases; the mean value (+/- 95% confidence interval) off for PCA < 1 h was 0.037 +/- 0.004, while that for PCA > 3 h was 0.12 +/- 0.04. This suggests that even in winter, photochemistry in urban environments can lead to increased thickly coated BC particles. The mean (+/- 95% confidence interval) enhancement in mass absorption cross-section (MAC) due to coatings on BC for our wintertime measurements in urban Los
机译：了解大气黑碳（BC）颗粒的物理和光学特性如何随时间和空间变化，对于减少气候强迫值（来自周围BC）的不确定性至关重要。在这项研究中，环境BC是在加利福尼亚鲁比多（Rubidoux）洛杉矶市区下风约90公里（55英里）处测量的。并置的NOx和NOy测量值用于估计采样空气的光化学年龄。在2015年2月3日至2015年3月12日之间的整天进行采样，以捕获周围BC的每日和每日变化。在15分钟的循环中对环境空气和热剥蚀的空气进行了采样，以比较涂层和未涂层​​BC颗粒的物理和光学性质。使用单颗粒煤灰光度计（SP2）测量单个BC颗粒的物理性质，包括质量和涂层厚度，并使用光声消光计（PAX）在870 nm下测量BC光学性质。活动的平均BC质量浓度（+/-标准偏差）为0.12 +/- 0.08μg m（-3）。尽管只有11:00和17:00 h之间的差异在统计学上是可区分的，但工作日的BC质量浓度高于周末。发现涂有厚涂层的总BC颗粒（f）的比例相对较低，在整个运动期间平均为0.05 +/- 0.02。通常在下午，光化学污染物浓度也达到最大值时，f值达到峰值。此外，发现周末的脂肪15：00-16：00 h在统计上要比工作日高，这可能是因为周末与工作日相比，周末的环境SOA与BC的相对量较高，这将增强主要BC颗粒的SOA涂层周末从洛杉矶西部盆地到我们采样点的运输过程中的年龄。尽管周末值系统性地较高，但是在一天的光化学活性期间（10:00 14:00 h）其他时间的差异没有统计学差异。将f与采样空气的光化学年龄（PCA）进行比较，结果表明f随着PCA的增加而增加； PCA <1 h的平均值（+/- 95％置信区间）off为0.037 +/- 0.004，而PCA> 3 h的平均值为0.12 +/- 0.04。这表明即使在冬天，城市环境中的光化学作用也可能导致厚涂层的BC颗粒增加。在洛杉矶市区进行冬季测量时，由于BC上的涂层，质量吸收横截面（MAC）的平均（+/- 95％置信区间）提高

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