Abstract
Although the characteristics of biomass burning events and the ambient ecosystem determine emitted smoke composition, the conditions that modulate the partitioning of black carbon (BC) and brown carbon (BrC) formation are not well understood, nor are the spatial or temporal frequency of factors driving smoke particle evolution, such as hydration, coagulation, and oxidation, all of which impact smoke radiative forcing. In situ data from surface observation sites and aircraft field campaigns offer deep insight into the optical, chemical, and microphysical traits of biomass burning (BB) smoke aerosols, such as single scattering albedo (SSA) and size distribution, but cannot by themselves provide robust statistical characterization of both emitted and evolved particles. Data from the NASA Earth Observing System’s Multi-Angle Imaging SpectroRadiometer (MISR) instrument can provide at least a partial picture of BB particle properties and their evolution downwind, once properly validated. Here we use in situ data from the joint NOAA/NASA 2019 Fire Influence on Regional to Global Environments Experiment-Air Quality (FIREX-AQ) field campaign to assess the strengths and limitations of MISR-derived constraints on particle size, shape, light-absorption, and its spectral slope, as well as plume height and associated wind vectors. Based on the satellite observations, we also offer inferences about aging mechanisms effecting downwind particle evolution, such as gravitational settling, oxidation, secondary particle formation, and the combination of particle aggregation and condensational growth. This work builds upon our previous study, adding confidence to our interpretation of the remote-sensing data based on an expanded suite of in situ measurements for validation. The satellite and in situ measurements offer similar characterizations of particle property evolution as a function of smoke age for the 06 August Williams Flats Fire, and most of the key differences in particle size and absorption can be attributed to differences in sampling and changes in the plume geometry between sampling times. Whereas the aircraft data provide validation for the MISR retrievals, the satellite data offer a spatially continuous mapping of particle properties over the plume, which helps identify trends in particle property downwind evolution that are ambiguous in the sparsely sampled aircraft transects. The MISR data record is more than two decades long, offering future opportunities to study regional wildfire plume behavior statistically, where aircraft data are limited or entirely lacking.
Highlights
Wildfire smoke emissions are a rich and complex mixture of gas and aerosol constituents, the impacts of which occur over wide temporal and spatial scales and can result in short-term regional air quality issues as well as climate forcing
To determine which aerosols could serve as CCN in the Williams Flats plume, we considered measurements at 1 s intervals from a DMT cloud condensation nuclei counter 100 (CCN-100) ([58]: CCN), which applies a thermal gradient across a continuous-flow diffusion chamber to create a supersaturated environment where water vapor can condense onto particles
We infer that: (1) VOC condensation and/or coagulation of particles act to increase retrieved effective particle size (REPS) in Region II compared to Region I; (2) gravitational settling leads to a preferential decrease in the fraction of large-sized particles in Region III compared to Region II; (3) there is an increase in the oxidation state of particles progressively downwind throughout the plume, reflected in the increased aerosol optical depth (AOD) of non-absorbing analogs; and (4) there may be differences in the emissions between the northern and southern hotspots, leading to observed differences in particle size and absorption
Summary
Wildfire smoke emissions are a rich and complex mixture of gas and aerosol constituents, the impacts of which occur over wide temporal and spatial scales and can result in short-term regional air quality issues as well as climate forcing. Our previous work, (Junghenn-Noyes et al, 2020 [35], Paper 1) represents the first part of this program It compares the height and particle property results and interpretations from NASA Earth Observing System’s Multi-Angle Imaging Spectrometer (MISR) instrument with detailed, near-coincident aircraft observations of three wildfire smoke plumes during the U.S Department of Energy’s 2013 Biomass Burning Observation Project (BBOP) field campaign [27,28]. Most of the aircraft instrument types used in FIREX-AQ are similar to those employed during BBOP, many of the instrument teams are different, and the FIREX-AQ campaign offered several additional validation resources, such as plume height, particle non-sphericity, and other lidar-retrieved measurements; the degree of flaming and smoldering measurements in the fire itself; and improved data on fuel type at the point of burning These additions improve our previous understanding of MISR’s ability to characterize wildfire plumes, compared to Paper 1, and. The bulk of the fire activity was confined to 02 through 09 August, at which point a large precipitation event stifled burning so that Tthhee fciorentwroalslienfgfefcaticvteolrys ebxethinignudisfihreedeimn issusibosneqs,useunct hdaayssb. uHronwinegveinr,terne-siintvyigaonrdatfiuonelatnydpec,rceaepninchgange both farcetqivuietyntrleysuanltedddirnamcoanttiicnaulleydfmoraanaggivemenenfitree,ffroerntds ethrirnoguguhse2l5esAs ufogruvsta,lbidyawtiohnichantyiminetoevr-ecro4m4,p0a0r0isons madeacbreestwheadenbuorbnseedrv[7a5t]i.oTnhsewfiirtehwsaigs nmifiancaagnetdtiwmiteh lbaogtsh. avTihatiisonstaunddyotnh-ethree-fgorroeunledvceornatgaeinsmthenet only near-mcoeitnhcoiddsenintcsluedt ionfgMheISliRcopantedr winasteitrudorobpsse,raviarttiaonnksefrrroemtartdhaenFt IdRroEpXs-,AbQuilcdainmgpaaidgirne:cthliene0,6aAndugust 2019 sfligignhiftictahnrtomuogph-utphe[7W5].ilHlioawmesveFrl,aatcstiFvierefirpelsuumppereinssicoennwtraasl nWotasohccinurgrtiongn dsutaritneg. tThhe eFINREAXS-AAQDC-8 aircraoftpceorantdiouncstoedn 0a6“Areumguostet. sTehnesifnuegl”s oinvveorlpvaesdswweirtehirnepsoervteedralyl ma miniuxteusreoof fthtiemMbeIrS,Rshoovrtergpraassss,,laignhdt obsersvlaesdh tfhroempllougmgiengfo, ranadfaulclohnoifuerrouosf osavmersptolirnyg[7a5p];psriomxiilamrlayt,etlhye 2MhOsDuISbsLeeqvuelen tIlGy.BPDyuerairnlyg ltahned time betwecoevneor btyspeervshatoiwons sth, eprluegmioengiseaommeixttruyrechofagnrgaesdslannodt,iscaevaabnlny,a,manodstelviekreglryeeans naeeredsleulletafoffowreisnt,da-nddriven advecfputoieonlndce(hrFoaisrgaaucptreienrie1st)wi.caHscbolauwsrsneifviincegart,,ifoaonsllosshwyosewtdembnylaw(FtheCreC,aSptg)lruammssoedgerpalaisnrsgtlaicnrldeev(pe[5ar8ols]p: Fepurrtiemile2asFricirloeyr).rDeloautgelares-afsiro-Pnaacbifliyc well between the two sets of observations for smoke of similar age
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