skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Assessment of online water-soluble brown carbon measuring systems for aircraft sampling
Abstract. Brown carbon (BrC) consists of particulate organic species that preferentially absorb light at visible and ultraviolet wavelengths. Ambient studies show that as a component of aerosol particles, BrC affects photochemical reaction rates and regional to global climate. Some organic chromophores are especially toxic, linking BrC to adverse health effects. The lack of direct measurements of BrC has limited our understanding of its prevalence, sources, evolution, and impacts. We describe the first direct, online measurements of water-soluble BrC on research aircraft by three separate instruments. Each instrument measured light absorption over a broad wavelength range using a liquid waveguide capillary cell (LWCC) and grating spectrometer, with particles collected into water by a particle-into-liquid sampler (CSU PILS-LWCC and NOAA PILS-LWCC) or a mist chamber (MC-LWCC). The instruments were deployed on the NSF C-130 aircraft during WE-CAN 2018 as well as the NASA DC-8 and the NOAA Twin Otter aircraft during FIREX-AQ 2019, where they sampled fresh and moderately aged wildfire plumes. Here, we describe the instruments, calibrations, data analysis and corrections for baseline drift and hysteresis. Detection limits (3σ) at 365 nm were 1.53 Mm−1 (MC-LWCC; 2.5 min sampling time), 0.89 Mm−1 (CSU PILS-LWCC; 30 s sampling time), and 0.03 Mm−1 (NOAA PILS-LWCC; 30 s sampling time). Measurement uncertainties were 28 % (MC-LWCC), 12 % (CSU PILS-LWCC), and 11 % (NOAA PILS-LWCC). The MC-LWCC system agreed well with offline measurements from filter samples, with a slope of 0.91 and R2=0.89. Overall, these instruments provide soluble BrC measurements with specificity and geographical coverage that is unavailable by other methods, but their sensitivity and time resolution can be challenging for aircraft studies where large and rapid changes in BrC concentrations may be encountered.  more » « less
Award ID(s):
1650786
PAR ID:
10310693
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Atmospheric Measurement Techniques
Volume:
14
Issue:
10
ISSN:
1867-8548
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; (, Atmospheric Chemistry and Physics)
    Abstract. Light absorbing organic carbon, or brown carbon (BrC), can be a significantcontributor to the visible light absorption budget. However, the sources ofBrC and the contributions of BrC to light absorption are not wellunderstood. Biomass burning is thought to be a major source of BrC.Therefore, as part of the WE-CAN (Western Wildfire Experiment for CloudChemistry, Aerosol Absorption and Nitrogen) study, BrC absorption data werecollected on board the National Science Foundation/National Center for Atmospheric Research (NSF/NCAR) C-130 aircraft as it intercepted smoke fromwildfires in the western US in July–August 2018. BrC absorptionmeasurements were obtained in near real-time using two techniques. The firstcoupled a particle-into-liquid sampler (PILS) with a liquid waveguidecapillary cell and a total organic carbon analyzer for measurements ofwater-soluble BrC absorption and WSOC (water-soluble organic carbon). Thesecond employed a custom-built photoacoustic aerosol absorption spectrometer(PAS) to measure total absorption at 405 and 660 nm. The PAS BrC absorption at 405 nm (PAS total Abs 405 BrC) was calculated by assuming the absorption determined by the PAS at 660 nm was equivalent to the black carbon (BC) absorption and the BC aerosol absorption Ångström exponent was 1. Data from the PILS and PAS were combined to investigate the water-soluble vs. total BrC absorption at 405 nm in the various wildfire plumes sampled during WE-CAN. WSOC, PILS water-soluble Abs 405, and PAS total Abs 405 tracked each other in and out of the smoke plumes. BrC absorption was correlated with WSOC (R2 value for PAS =0.42 and PILS =0.60) and CO (carbon monoxide) (R2 value for PAS =0.76 and PILS =0.55) for all wildfires sampled. The PILS water-soluble Abs 405 was corrected for thenon-water-soluble fraction of the aerosol using the calculated UHSAS(ultra-high-sensitivity aerosol spectrometer) aerosol mass. The correctedPILS water-soluble Abs 405 showed good closure with the PAS total Abs 405BrC with a factor of ∼1.5 to 2 difference. This differencewas explained by particle vs. bulk solution absorption measured by the PASvs. PILS, respectively, and confirmed by Mie theory calculations. DuringWE-CAN, ∼ 45 % (ranging from 31 % to 65 %) of the BrCabsorption was observed to be due to water-soluble species. The ratio of BrC absorption to WSOC or ΔCO showed no clear dependence on firedynamics or the time since emission over 9 h. 
    more » « less
  2. ; ; ; ; ; ; (, Atmospheric Environment)
    Brown carbon (BrC) plays an important role in global radiative budget but there have been few studies on BrC in Arctic despite rapid warming and increasing wildfires in this region. Here we investigate the optical properties of BrC from boreal fires in Alaska summer, with two sets of measurements from PILS-LWCC-TOC (Particle-Into-Liquid-Sampler – Liquid-Waveguide Capillary flow-through optical Cell - Total-Organic-Carbon analyzer) and filter measurements. We show that during intense wildfires, the mass absorption coefficient at 365 nm (MAC365) from water soluble organic carbon (WSOC) remained stable at ∼1 m2 g−1. With all plumes sampled and derived transport time, we show a decrease of MAC365 with plume age, with a shorter photobleaching lifetime (∼11 h) at 365 nm compared to 405 nm (∼20 h). The total absorption by organic aerosols measured from filters at 365 nm is higher than the absorption by WSOC by a factor 2–3, suggesting a dominant role of insoluble organic carbon. Overall BrC dominates absorption in the near-ultraviolet and visible radiation during wildfire season in Alaska summer. 
    more » « less
  3. ; ; ; ; ; ; ; (, Communications Chemistry)
    Abstract Nitrogen-containing organic carbon (NOC) in atmospheric particles is an important class of brown carbon (BrC). Redox active NOC like aminophenols received little attention in their ability to form BrC. Here we show that iron can catalyze dark oxidative oligomerization ofo- andp-aminophenols under simulated aerosol and cloud conditions (pH 1–7, and ionic strength 0.01–1 M). Homogeneous aqueous phase reactions were conducted using soluble Fe(III), where particle growth/agglomeration were monitored using dynamic light scattering. Mass yield experiments of insoluble soot-like dark brown to black particles were as high as 40%. Hygroscopicity growth factors (κ) of these insoluble products under sub- and super-saturated conditions ranged from 0.4–0.6, higher than that of levoglucosan, a prominent proxy for biomass burning organic aerosol (BBOA). Soluble products analyzed using chromatography and mass spectrometry revealed the formation of ring coupling products ofo- andp-aminophenols and their primary oxidation products. Heterogeneous reactions of aminophenol were also conducted using Arizona Test Dust (AZTD) under simulated aging conditions, and showed clear changes to optical properties, morphology, mixing state, and chemical composition. These results highlight the important role of iron redox chemistry in BrC formation under atmospherically relevant conditions. 
    more » « less
  4. ; ; ; ; ; ; (, Atmospheric Chemistry and Physics)
    Abstract. The methanol extraction method was widely applied to isolate organic carbon(OC) from ambient aerosols, followed by measurements of brown carbon (BrC)absorption. However, undissolved OC fractions will lead to underestimatedBrC absorption. In this work, water, methanol (MeOH), MeOH / dichloromethane(MeOH / DCM, 1:1, v/v), MeOH / DCM (1:2, v/v), tetrahydrofuran (THF), andN,N-dimethylformamide (DMF) were tested for extraction efficiencies ofambient OC, and the light absorption of individual solvent extracts wasdetermined. Among the five solvents and solvent mixtures, DMF dissolved thehighest fractions of ambient OC (up to ∼95 %), followed byMeOH and MeOH / DCM mixtures (<90 %), and the DMF extracts hadsignificantly (p<0.05) higher light absorption than other solventextracts. This is because the OC fractions evaporating at highertemperatures (>280∘) are less soluble in MeOH(∼80 %) than in DMF (∼90 %) and containstronger light-absorbing chromophores. Moreover, the light absorption of DMFand MeOH extracts of collocated aerosol samples in Nanjing showed consistenttemporal variations in winter when biomass burning dominated BrC absorption, while the average light absorption of DMF extracts was more than 2 timesgreater than the MeOH extracts in late spring and summer. The average lightabsorption coefficient at 365 nm of DMF extracts was 30.7 % higher (p<0.01) than that of MeOH extracts. Source apportionment resultsindicated that the MeOH solubility of BrC associated with biomass burning,lubricating oil combustion, and coal combustion is similar to their DMFsolubility. The BrC linked with unburned fossil fuels and polymerizationprocesses of aerosol organics was less soluble in MeOH than in DMF, whichwas likely the main reason for the large difference in time series betweenMeOH and DMF extract absorption. These results highlight the importance oftesting different solvents to investigate the structures and lightabsorption of BrC, particularly for the low-volatility fraction potentiallyoriginating from non-combustion sources. 
    more » « less
  5. ; ; ; ; (, Environmental Science: Atmospheres)
    The light-absorption properties of brown carbon (BrC) are often estimated using offline, solvent-extraction methods. However, recent studies have found evidence of insoluble BrC species that are unaccounted for in solvent extraction. In this work, we produced carbonaceous aerosol particles from the combustion of three biomass fuels (pine needles, hickory twigs, and oak foliage). We utilized a combination of online and offline measurements and optical calculations to estimate the mass fractions and contribution to light absorption by methanol-soluble BrC (MSBrC), methanol-insoluble BrC (MIBrC), and elemental carbon (EC). Averaged over all experiments, the majority of the carbonaceous aerosol species were attributed to MSBrC (90% ± 5%), while MIBrC and EC constituted 9% ± 5% and 1% ± 0.5%, respectively. The BrC produced in all experiments was moderately absorbing, with an imaginary component of the refractive index ( k ) at 532 nm ranging between 0.01 and 0.05. However, the k values at 532 nm of the MSBrC (0.004 ± 0.002) and MIBrC (0.211 ± 0.113) fractions were separated by two orders of magnitude, with MSBrC categorized as weakly absorbing BrC and MIBrC as strongly absorbing BrC. Consequently, even though MSBrC constituted the majority of the aerosol mass, MIBrC had a dominant contribution to light absorption at 532 nm (72% ± 11%). The findings presented in this paper provide support for previous reports of the existence of strongly absorbing, methanol-insoluble BrC species and indicate that relying on methanol extraction to characterize BrC in biomass-burning emissions would severely underestimate its absorption. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email