scholarly journals Three years of measurements of light-absorbing aerosols over coastal Namibia: seasonality, origin, and transport

2018 ◽  
Vol 18 (23) ◽  
pp. 17003-17016 ◽  
Author(s):  
Paola Formenti ◽  
Stuart John Piketh ◽  
Andreas Namwoonde ◽  
Danitza Klopper ◽  
Roelof Burger ◽  
...  
Keyword(s):  
Black Carbon ◽  
Biomass Burning ◽  
Marine Boundary Layer ◽  
Sampling Period ◽  
Dry Season ◽  
Back Trajectories ◽  
Microphysical Properties ◽  
Maritime Traffic ◽  
Stratocumulus Clouds ◽  
Absorbing Aerosols

Abstract. Continuous measurements between July 2012 and December 2015 at the Henties Bay Aerosol Observatory (HBAO; 22∘ S, 14∘05′ E), Namibia, show that, during the austral wintertime, transport of light-absorbing black carbon aerosols occurs at low level into the marine boundary layer. The average of daily concentrations of equivalent black carbon (eBC) over the whole sampling period is 53 (±55) ng m−3. Peak values above 200 ng m−3 and up to 800 ng m−3 occur seasonally from May to August, ahead of the dry season peak of biomass burning in southern Africa (August to October). Analysis of 3-day air mass back-trajectories show that air masses from the South Atlantic Ocean south of Henties Bay are generally cleaner than air having originated over the ocean north of Henties Bay, influenced by the outflow of the major biomass burning plume, and from the continent, where wildfires occur. Additional episodic peak concentrations, even for oceanic transport, indicate that pollution from distant sources in South Africa and maritime traffic along the Atlantic ship tracks could be important. While we expect the direct radiative effect to be negligible, the indirect effect on the microphysical properties of the stratocumulus clouds and the deposition to the ocean could be significant and deserve further investigation, specifically ahead of the dry season.

scholarly journals Effect of biomass burning on marine stratocumulus clouds off the California coast

2009 ◽  
Vol 9 (22) ◽  
pp. 8841-8856 ◽  
Author(s):  
J. Brioude ◽  
O. R. Cooper ◽  
G. Feingold ◽  
M. Trainer ◽  
S. R. Freitas ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Marine Boundary Layer ◽  
Cloud Fraction ◽  
Marine Stratocumulus ◽  
Cloud Albedo ◽  
Stratocumulus Clouds ◽  
Absorbing Aerosols ◽  
Indirect Radiative Forcing

Abstract. Aerosol-cloud interactions are considered to be one of the most important and least known forcings in the climate system. Biomass burning aerosols are of special interest due to their radiative impact (direct and indirect effect) and their potential to increase in the future due to climate change. Combining data from Geostationary Operational Environmental Satellite (GOES) and MODerate-resolution Imaging Spectroradiometer (MODIS) with passive tracers from the FLEXPART Lagrangian Particle Dispersion Model, the impact of biomass burning aerosols on marine stratocumulus clouds has been examined in June and July of 2006–2008 off the California coast. Using a continental tracer, the indirect effect of biomass burning aerosols has been isolated by comparing the average cloud fraction and cloud albedo for different meteorological situations, and for clean versus polluted (in terms of biomass burning) continental air masses at 14:00 local time. Within a 500 km-wide band along the coast of California, biomass burning aerosols, which tend to reside above the marine boundary layer, increased the cloud fraction by 0.143, and the cloud albedo by 0.038. Absorbing aerosols located above the marine boundary layer lead to an increase of the lower tropospheric stability and a reduction in the vertical entrainment of dry air from above, leading to increased cloud formation. The combined effect was an indirect radiative forcing of −7.5% ±1.7% (cooling effect) of the outgoing radiative flux at the top of the atmosphere on average, with a bias due to meteorology of +0.9%. Further away from the coast, the biomass burning aerosols, which were located within the boundary layer, reduced the cloud fraction by 0.023 and the cloud albedo by 0.006, resulting in an indirect radiative forcing of +1.3% ±0.3% (warming effect) with a bias of +0.5%. These results underscore the dual role that absorbing aerosols play in cloud radiative forcing.

Low Cloud Cover Sensitivity to Biomass-Burning Aerosols and Meteorology over the Southeast Atlantic

2018 ◽  
Vol 31 (11) ◽  
pp. 4329-4346 ◽  
Author(s):  
Adeyemi A. Adebiyi ◽  
Paquita Zuidema
Keyword(s):  
Biomass Burning ◽  
Cloud Cover ◽  
Longwave Radiation ◽  
Cloud Fraction ◽  
Specific Humidity ◽  
Aerosol Layer ◽  
Stratocumulus Clouds ◽  
Low Cloud ◽  
Low Cloud Cover ◽  
Absorbing Aerosols

Abstract Shortwave-absorbing aerosols seasonally cover and interact with an expansive low-level cloud deck over the southeast Atlantic. Daily anomalies of the MODIS low cloud fraction, fine-mode aerosol optical depth (AODf), and six ERA-Interim meteorological parameters (lower-tropospheric stability, 800-hPa subsidence, 600-hPa specific humidity, 1000- and 800-hPa horizontal temperature advection, and 1000-hPa geopotential height) are constructed spanning July–October (2001–12). A standardized multiple linear regression, whereby the change in the low cloud fraction to each component’s variability is normalized by one standard deviation, facilitates comparison between the different variables. Most cloud–meteorology relationships follow expected behavior for stratocumulus clouds. Of interest is the low cloud–subsidence relationship, whereby increasing subsidence increases low cloud cover between 10° and 20°S but decreases it elsewhere. Increases in AODf increase cloudiness everywhere, independent of other meteorological predictors. The cloud–AODf effect is partially compensated by accompanying increases in the midtropospheric moisture, which is associated with decreases in low cloud cover. This suggests that the free-tropospheric moisture affects the low cloud deck primarily through longwave radiation rather than mixing. The low cloud cover is also more sensitive to aerosol when the vertical distance between the cloud and aerosol layer is relatively small, which is more likely to occur early in the biomass burning season and farther offshore. A parallel statistical analysis that does not include AODf finds altered relationships between the low cloud cover changes and meteorology that can be understood through the aerosol cross-correlations with the meteorological predictors. For example, the low cloud–stability relationship appears stronger if aerosols are not explicitly included.

scholarly journals Observations of Supermicron-Sized Aerosols Originating from Biomass Burning in South Central Africa

2021 ◽  
Author(s):  
Rose Marie Miller ◽  
Greg M. McFarquhar ◽  
Robert M. Rauber ◽  
Joseph R. O'Brien ◽  
Siddhant Gupta ◽  
...  
Keyword(s):  
Black Carbon ◽  
Biomass Burning ◽  
Single Particle ◽  
Central Africa ◽  
Submicron Particles ◽  
Back Trajectories ◽  
Active Fire ◽  
South Central ◽  
Moderate Resolution ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. During the three years of the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) campaign, the NASA Orion P-3 was equipped with a 2D-Stereo (2D-S) probe that imaged particles with maximum dimension (D) ranging from 10 < D < 1280 µm. The 2D-S recorded supermicron-sized aerosol particles (SAPs) outside of clouds within biomass burning plumes during flights over the Southeast Atlantic off Africa’s coast. Numerous SAPs with 10 < D < 1520 µm were observed in 2017 and 2018 at altitudes between 1230 m and 3500 m, 1000 km from the coastline mostly between 7–11° S. No SAPs were observed in 2016 as flights were conducted further south and further from the coastline. Number concentrations of black carbon (rBC) measured by a single particle soot photometer ranged from 200 to 1200 cm−3 when SAPs were observed. Transmission electron microscopy images of submicron particulates, collected on Holey carbon grid filters, revealed particles with potassium salts, black carbon and organics while energy-dispersive X-ray spectroscopy spectra detected potassium, a tracer for biomass burning, indicating that the submicron particles originated from biomass burning in addition to black carbon. NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) three-day back trajectories show a source in northern Angola for times when large SAPs were observed. Fire Information for Resource Management System Moderate Resolution Imaging Spectroradiometer (MODIS) 6 active fire maps showed extensive biomass burning at these locations. Given the back trajectories, the high number concentrations of rBC, and the presence of elemental tracers indicative of biomass burning, it is hypothesized that the SAPs imaged by the 2D-S are examples of unburned plant material previously seen in biomass burning smoke close to the source.

scholarly journals Vertical variability of the properties of highly aged biomass burning aerosol transported over the southeast Atlantic during CLARIFY-2017

2020 ◽  
Author(s):  
Huihui Wu ◽  
Jonathan W. Taylor ◽  
Kate Szpek ◽  
Justin Langridge ◽  
Paul I. Williams ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
Regional Climate ◽  
Single Scattering ◽  
Important Region ◽  
Absorbing Aerosols ◽  
Lower Temperature ◽  
The Impact ◽  
Vertical Variability

Abstract. Seasonal biomass burning (BB) from June to October in central and southern Africa leads to absorbing aerosols being transported over the south Atlantic Ocean every year, and contributes significantly to the regional climate forcing. The vertical distribution of submicron aerosols and their properties were characterized over the remote southeast Atlantic for the first time, using airborne in-situ measurements made during the CLoud-Aerosol-Radiation Interactions and Forcing for Year 2017 (CLARIFY-2017) campaign. BB aerosols were intensively observed in the region surrounding Ascension Island, in the marine boundary layer (MBL) and free troposphere (FT) up to 5 km. We show that the aerosols had undergone a significant aging process during > 7 days transit from source, as indicated by highly oxidized organic aerosol and thickly coated black carbon (BC). The highly aged BB aerosols in the CLARIFY region were also especially rich in BC compared with those from other regions. We also found significant vertical variation in the single scattering albedos (SSA) of these aerosols, as a function of relative chemical composition and size. The lowest SSA was generally in the low FT layer around 2000 m altitude (medians: 0.83 at 405 nm and 0.80 at 658 nm). This finding is important since it means that BB aerosols across the east Atlantic region are more absorbing than is currently represented in climate models. Furthermore, in the FT, we show that SSA increased with altitude and this was associated with an enhanced inorganic nitrate mass fraction and aerosol size. This likely results from increased partitioning to the existing particles at higher altitude with lower temperature and higher relative humidity. After entrainment into the BL, aerosols were generally smaller in size than were observed in the FT, and had a larger fraction of scattering material with resultant higher average dry SSA, mostly due to marine emissions and aerosol removal by drizzle. Our results provide unique observational constraints on aerosol parameterizations used in modelling regional radiation interactions over this important region. We recommend that future work should consider the impact of this vertical variability on climate models.

scholarly journals Fire in ice: two millennia of boreal forest fire history from the Greenland NEEM ice core

2014 ◽  
Vol 10 (5) ◽  
pp. 1905-1924 ◽  
Author(s):  
P. Zennaro ◽  
N. Kehrwald ◽  
J. R. McConnell ◽  
S. Schüpbach ◽  
O. J. Maselli ◽  
...  
Keyword(s):  
Black Carbon ◽  
Biomass Burning ◽  
High Latitude ◽  
Fire History ◽  
Global Climate ◽  
Ice Cores ◽  
Back Trajectories ◽  
The Past ◽  
Isotopic Analyses ◽  
Fire Activity

Abstract. Biomass burning is a major source of greenhouse gases and influences regional to global climate. Pre-industrial fire-history records from black carbon, charcoal and other proxies provide baseline estimates of biomass burning at local to global scales spanning millennia, and are thus useful to examine the role of fire in the carbon cycle and climate system. Here we use the specific biomarker levoglucosan together with black carbon and ammonium concentrations from the North Greenland Eemian (NEEM) ice cores (77.49° N, 51.2° W; 2480 m a.s.l) over the past 2000 years to infer changes in boreal fire activity. Increases in boreal fire activity over the periods 1000–1300 CE and decreases during 700–900 CE coincide with high-latitude NH temperature changes. Levoglucosan concentrations in the NEEM ice cores peak between 1500 and 1700 CE, and most levoglucosan spikes coincide with the most extensive central and northern Asian droughts of the past millennium. Many of these multi-annual droughts are caused by Asian monsoon failures, thus suggesting a connection between low- and high-latitude climate processes. North America is a primary source of biomass burning aerosols due to its relative proximity to the Greenland Ice Cap. During major fire events, however, isotopic analyses of dust, back trajectories and links with levoglucosan peaks and regional drought reconstructions suggest that Siberia is also an important source of pyrogenic aerosols to Greenland.

scholarly journals Vertical structure of biomass burning aerosol transported over the southeast Atlantic Ocean

2021 ◽  
Author(s):  
Harshvardhan Harshvardhan ◽  
Richard Ferrare ◽  
Sharon Burton ◽  
Johnathan Hair ◽  
Chris Hostetler ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
High Spectral Resolution ◽  
Aerosol Layer ◽  
Aerosol Extinction ◽  
Microphysical Properties ◽  
Stratocumulus Clouds ◽  
Fine Mode ◽  
Cloud Tops

Abstract. Biomass burning in southwestern Africa produces smoke plumes that are transported over the Atlantic Ocean and overlie vast regions of stratocumulus clouds. This aerosol layer contributes to direct and indirect radiative forcing of the atmosphere in this region, particularly during the months of August, September and October. There was a multi-year international campaign to study this aerosol and its interactions with clouds. Here we report on the evolution of aerosol distributions and properties as measured by the airborne high spectral resolution lidar (HSRL) during the ORACLES (Observations of Aerosols above Clouds and their intEractionS) campaign in September 2016. The NASA Langley HSRL-2 instrument was flown on the NASA ER-2 aircraft for several days in September 2016. Data were aggregated at two pairs of 2° × 2° grid boxes to examine the evolution of the vertical profile of aerosol properties during transport over the ocean. Results showed that the structure of the profile of aerosol extinction and microphysical properties is maintained over a one to two-day time scale. The fraction of aerosol in the fine mode between 50 and 500 nm remained above 0.95 and the effective radius of this fine mode was 0.16 μm from 3 to 5 km in altitude. This indicates that there is essentially no scavenging or dry deposition at these altitudes. Moreover, there is very little day to day variation in these properties, such that time sampling as happens in such campaigns, may be representative of longer periods such as monthly means. Below 3 km there is considerable mixing with larger aerosol, most likely continental source near land. Furthermore, these measurements indicated that there was a distinct gap between the bottom of the aerosol layer and cloud tops at the selected locations as evidenced by a layer of several hundred meters that contained relatively low aerosol extinction values above the clouds.

scholarly journals Size-resolved observations of refractory black carbon particles in cloud droplets at a marine boundary layer site

2014 ◽  
Vol 14 (8) ◽  
pp. 11447-11491 ◽  
Author(s):  
J. C. Schroder ◽  
S. J. Hanna ◽  
R. L. Modini ◽  
A. L. Corrigan ◽  
A. M. Macdonald ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Marine Boundary Layer ◽  
Back Trajectory ◽  
Cloud Droplets ◽  
Back Trajectories ◽  
Air Masses ◽  
Carbon Particles ◽  
Back Trajectory Analysis ◽  
La Jolla

Abstract. Size resolved observations of aerosol particles (including black carbon particles) and cloud residuals were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, CA during 2012. A counterflow virtual impactor was used to sample cloud residuals while a total inlet was used to sample both cloud residuals and interstitial particles. Two cloud events totaling ten hours of in-cloud sampling were analyzed. Since the CVI only sampled cloud droplets larger than &amp;approx;11 μm, less than 100% of the cloud droplets were sampled during the two cloud events (&amp;approx;38% of the cloud droplets for the first cloud event and &amp;approx;24% of the cloud droplets for the second cloud were sampled). Back trajectories showed that air masses for both cloud events spent at least 96 h over the Pacific Ocean and traveled near, or over populated regions just before sampling. Based on bulk aerosol particle concentrations measured from the total inlet the two air masses sampled were classified as polluted marine air, a classification that was consistent with back trajectory analysis and the mass concentrations of refractory black carbon (rBC) measured from the total inlet. The activated fraction of rBC, estimated from the measurements, ranged from 0.01 to 0.1 for core diameters ranging from 70 to 220 nm. Since the fraction of cloud droplets sampled by the CVI was less than 100%, the measured activated fractions of rBC should be considered as lower limits to the total fraction of rBC activated during the two cloud events. Size distributions of rBC sampled from the residual inlet show that sub-100 nm rBC cores were incorporated into the droplets in both clouds. The coating analysis shows that the rBC cores had average coating thicknesses of 75 nm for core diameters of 70 nm and 29 nm for core diameters of 220 nm. The presence of sub-100 nm rBC cores in the cloud residuals is consistent with kappa-Köhler theory and the measured coating thicknesses of the rBC cores.

scholarly journals Black carbon over the South China Sea and in various continental locations in South China

2013 ◽  
Vol 13 (24) ◽  
pp. 12257-12270 ◽  
Author(s):  
D. Wu ◽  
C. Wu ◽  
B. Liao ◽  
H. Chen ◽  
M. Wu ◽  
...  
Keyword(s):  
South China Sea ◽  
Black Carbon ◽  
South China ◽  
Rainy Season ◽  
Sampling Period ◽  
Dry Season ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Urban Sites

Abstract. Black carbon (BC) is an important atmospheric constituent as an air pollutant and as a climate forcer. To our knowledge, field measurements of BC have not been reported over the South China Sea. Observations of light-absorption coefficients (σabs) and BC concentrations by Aethalometer were conducted on Yongxing Island in the South China Sea and at five continental sites in the Pearl River delta (PRD) region, South China, in two periods: 16 May–20 June 2008 in the rainy season and 12 December 2008–8 January 2009 in the dry season. At the oceanic site, the daily average BC concentrations varied from 0.28 to 2.14 μg m−3 and variations of BC were small between the two periods (0.67 in the dry season sampling period and 0.54 μg m−3 in the rainy season sampling period). Similarly, little difference in BC level was found at a rural site in PRD between the two sampling periods (2.88 and 2.62 μg m–3). At the PRD urban sites, the daily average concentration of BC ranged from 1.56 to 37.9 μg m−3, higher in the dry season sampling period (12.31 μg m–3) and lower in the rainy season sampling period (6.17 μg m–3). The observed average σabs values in rainy vs. dry season sampling periods are 119 vs. 62 Mm−1 at the PRD urban sites, 29 vs. 26 Mm−1 at the PRD background site, and 8.4 vs. 7.2 Mm−1 at the marine site. At urban/suburban PRD sites, BC was observed to have a diurnal pattern of higher concentrations at night and at the urban sites a small peak in the early morning rush hour.

scholarly journals Measurements to determine the mixing state of black carbon emitted from the 2017–2018 California wildfires and urban Los Angeles

2020 ◽  
Vol 20 (24) ◽  
pp. 15635-15664
Author(s):  
Joseph Ko ◽  
Trevor Krasowsky ◽  
George Ban-Weiss
Keyword(s):  
Los Angeles ◽  
Black Carbon ◽  
Biomass Burning ◽  
Spatial Scales ◽  
Field Measurements ◽  
Mixing State ◽  
Air Masses ◽  
Microphysical Properties ◽  
Source Type ◽  
Wide Variability

Abstract. The effects of atmospheric black carbon (BC) on climate and public health have been well established, but large uncertainties remain regarding the extent of the impacts of BC at different temporal and spatial scales. These uncertainties are largely due to the heterogeneous nature of BC in terms of its spatiotemporal distribution, mixing state, and coating composition. Here, we seek to further understand the size and mixing state of BC emitted from various sources and aged over different timescales using field measurements in the Los Angeles region. We measured refractory black carbon (rBC) with a single-particle soot photometer (SP2) on Catalina Island, California (∼70 km southwest of downtown Los Angeles) during three different time periods. During the first campaign (September 2017), westerly winds were dominant and measured air masses were representative of well-aged background over the Pacific Ocean. In the second and third campaigns (December 2017 and November 2018, respectively), atypical Santa Ana wind conditions allowed us to measure biomass burning rBC (BCbb) from air masses dominated by large biomass burning events in California and fossil fuel rBC (BCff) from the Los Angeles Basin. We observed that the emissions source type heavily influenced both the size distribution of the rBC cores and the rBC mixing state. BCbb had thicker coatings and larger core diameters than BBff. We observed a mean coating thickness (CTBC) of ∼40–70 nm and a count mean diameter (CMD) of ∼120 nm for BCbb. For BCff, we observed a CTBC of ∼5–15 nm and a CMD of ∼100 nm. Our observations also provided evidence that aging led to an increased CTBC for both BCbb and BCff. Aging timescales < ∼1 d were insufficient to thickly coat freshly emitted BCff. However, CTBC for aged BCff within aged background plumes was ∼35 nm thicker than CTBC for fresh BCff. Likewise, we found that CTBC for aged BCbb was ∼18 nm thicker than CTBC for fresh BCbb. The results presented in this study highlight the wide variability in the BC mixing state and provide additional evidence that the emissions source type and aging influence rBC microphysical properties.

scholarly journals Size-resolved observations of refractory black carbon particles in cloud droplets at a marine boundary layer site

2015 ◽  
Vol 15 (3) ◽  
pp. 1367-1383 ◽  
Author(s):  
J. C. Schroder ◽  
S. J. Hanna ◽  
R. L. Modini ◽  
A. L. Corrigan ◽  
S. M. Kreidenwies ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Marine Boundary Layer ◽  
Volume Fraction ◽  
Particle Diameter ◽  
Cloud Droplet ◽  
Cloud Droplets ◽  
Back Trajectories ◽  
Carbon Particles ◽  
La Jolla

Abstract. Size-resolved observations of aerosol particles and cloud droplet residuals were studied at a marine boundary layer site (251 m a.m.s.l.) in La Jolla, San Diego, California, during 2012. A counterflow virtual impactor (CVI) was used as the inlet to sample cloud residuals while a total inlet was used to sample both cloud residuals and interstitial particles. Two cloud events totaling 10 h of in-cloud sampling were analyzed. Based on bulk aerosol particle concentrations, mass concentrations of refractory black carbon (rBC), and back trajectories, the two air masses sampled were classified as polluted marine air. Since the fraction of cloud droplets sampled by the CVI was less than 100%, the measured activated fractions of rBC should be considered as lower limits to the total fraction of rBC activated during the two cloud events. Size distributions of rBC and a coating analysis showed that sub-100 nm rBC cores with relatively thick coatings were incorporated into the cloud droplets (i.e., 95 nm rBC cores with median coating thicknesses of at least 65 nm were incorporated into the cloud droplets). Measurements also show that the coating volume fraction of rBC cores is relatively large for sub-100 nm rBC cores. For example, the median coating volume fraction of 95 nm rBC cores incorporated into cloud droplets was at least 0.9, a result that is consistent with κ-Köhler theory. Measurements of the total diameter of the rBC-containing particles (rBC core and coating) suggest that the total diameter of rBC-containing particles needed to be at least 165 nm to be incorporated into cloud droplets when the core rBC diameter is ≥ 85 nm. This result is consistent with previous work that has shown that particle diameter is important for activation of non-rBC particles. The activated fractions of rBC determined from the measurements ranged from 0.01 to 0.1 for core rBC diameters ranging from 70 to 220 nm. This type of data is useful for constraining models used for predicting rBC concentrations in the atmosphere.

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