气候变化领域集成服务门户(CCPortal): Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic

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DOI	10.5194/acp-20-2341-2020
	Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic
	Pennypacker S.; DIamond M.; Wood R.
发表日期	2020
ISSN	16807316
起始页码	2341
结束页码	2351
卷号	20 期号:4
英文摘要	We study 41 d with daily median surface accumulation mode aerosol particle concentrations below 50 cm-3 (ultra-clean conditions) observed at Ascension Island (ASI; 7.9_ S, 14.4_ W) between June 2016 and October 2017 as part of the Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign. Interestingly, these days occur during a period of great relevance for aerosol-cloud-radiation interactions, the southeast Atlantic (SEATL) biomass-burning season (approximately June-October). That means that these critical months can feature both the highest surface aerosol numbers, from smoke intrusion into the marine boundary layer, as well as the lowest. While carbon monoxide and refractory black carbon concentrations on ultra-clean days do not approach those on days with heavy smoke, they also frequently exceed background concentrations calculated in the non-burning season from December 2016 to April 2017. This is evidence that even what become ultra-clean boundary layers can make contact with and entrain from an overlying SEATL smoke layer before undergoing a process of rapid aerosol removal. Because many ultra-clean and polluted boundary layers observed at Ascension Island during the biomass burning season follow similar isobaric back trajectories, the variability in this entrainment is likely more closely tied to the variability in the overlying smoke rather than large-scale horizontal circulation through the boundary layer. Since exceptionally low accumulation mode aerosol numbers at ASI do not necessarily indicate the relative lack of other trace pollutants, this suggests the importance of regional variations in what constitutes an "ultra-clean" marine boundary layer. Finally, surface drizzle rates, frequencies and accumulation - as well as retrievals of liquid water path - all consistently tend toward higher values on ultraclean days. This implicates enhanced coalescence scavenging in low clouds as the key driver of ultra-clean events in the southeast Atlantic marine boundary layer. These enhancements occur against and are likely mediated by the backdrop of a seasonal increase in daily mean cloud fraction and daily median liquid water path over ASI, peaking in September and October in both LASIC years. Therefore the seasonality in ultra-clean day occurrence seems directly linked to the seasonality in SEATL cloud properties. These results highlight the importance of two-way aerosol-cloud interactions in the region. © 2020 BMJ Publishing Group. All rights reserved.
关键词	aerosol biomass burning boundary layer carbon monoxide cloud concentration (composition)electromagnetic radiation marine atmosphere smoke Ascension Island Atlantic Ocean Atlantic Ocean (Southeast)
语种	英语
来源机构	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/132210
推荐引用方式 GB/T 7714	Pennypacker S.,DIamond M.,Wood R.. Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic[J]. Atmospheric Chemistry and Physics,2020,20(4).
APA	Pennypacker S.,DIamond M.,&Wood R..(2020).Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic.,20(4).
MLA	Pennypacker S.,et al."Ultra-clean and smoky marine boundary layers frequently occur in the same season over the southeast Atlantic".20.4(2020).