Showing papers by "Robert J. Yokelson published in 2020"
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TL;DR: In this article, the authors explored the molecular composition of light-absorbing organic aerosol, or brown carbon (BrC), sampled at the Missoula Fire Sciences laboratory as a part of the FIREX Fall 2016 lab intensive.
Abstract: . To better understand the effects of wildfires on air quality and
climate, it is important to assess the occurrence of chromophoric compounds
in smoke and characterize their optical properties. This study explores the
molecular composition of light-absorbing organic aerosol, or brown carbon
(BrC), sampled at the Missoula Fire Sciences laboratory as a part of the
FIREX Fall 2016 lab intensive. A total of 12 biomass fuels from different plant
types were tested, including gymnosperm (coniferous) and angiosperm
(flowering) plants and different ecosystem components such as duff, litter,
and canopy. Emitted biomass burning organic aerosol (BBOA) particles were
collected onto Teflon filters and analyzed offline using high-performance
liquid chromatography coupled to a photodiode array spectrophotometer and a high-resolution mass spectrometer
(HPLC–PDA–HRMS). Separated BrC chromophores were classified by their
retention times, absorption spectra, integrated absorbance in the near-UV
and visible spectral range (300–700 nm), and chemical formulas from the
accurate m∕z measurements. BrC chromophores were grouped into the following
classes and subclasses: lignin-derived products, which include lignin pyrolysis
products; distillation products, which include coumarins and flavonoids;
nitroaromatics; and polycyclic aromatic hydrocarbons (PAHs). The observed
classes and subclasses were common across most fuel types, although specific BrC
chromophores varied based on plant type (gymnosperm or angiosperm) and
ecosystem component(s) burned. To study the stability of the observed BrC
compounds with respect to photodegradation, BBOA particle samples were
irradiated directly on filters with near UV (300–400 nm) radiation, followed
by extraction and HPLC–PDA–HRMS analysis. Lifetimes of individual BrC
chromophores depended on the fuel type and the corresponding combustion
condition. Lignin-derived and flavonoid classes of BrC generally had
the longest lifetimes with respect to UV photodegradation. Moreover,
lifetimes for the same type of BrC chromophores varied depending on biomass
fuel and combustion conditions. While individual BrC chromophores
disappeared on a timescale of several days, the overall light absorption by
the sample persisted longer, presumably because the condensed-phase
photochemical processes converted one set of chromophores into another
without complete photobleaching or from undetected BrC chromophores that
photobleached more slowly. To model the effect of BrC on climate, it is
important to understand the change in the overall absorption coefficient
with time. We measured the equivalent atmospheric lifetimes of the overall
BrC absorption coefficient, which ranged from 10 to 41 d, with subalpine
fir having the shortest lifetime and conifer canopies, i.e., juniper, having
the longest lifetime. BrC emitted from biomass fuel loads encompassing
multiple ecosystem components (litter, shrub, canopy) had absorption
lifetimes on the lower end of the range. These results indicate that
photobleaching of BBOA by condensed-phase photochemistry is
relatively slow. Competing chemical aging mechanisms, such as heterogeneous
oxidation by OH, may be more important for controlling the rate of BrC
photobleaching in BBOA.
109 citations
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Brookhaven National Laboratory1, Japan Meteorological Agency2, Arizona State University3, University of California, Davis4, California Air Resources Board5, Los Alamos National Laboratory6, Colorado State University7, Pacific Northwest National Laboratory8, Washington University in St. Louis9, Syracuse University10, University of Montana11
TL;DR: In the first phase of the Biomass Burn Operational Project (BBOP) field campaign, conducted in the Pacific Northwest, the DOE G-1 aircraft was used to follow the time evolution of wildfire smoke from near the point of emission to locations 2.5 hours downwind as mentioned in this paper.
Abstract: . During the first phase of the Biomass Burn Operational Project (BBOP) field campaign, conducted in the Pacific Northwest, the DOE G-1 aircraft was used to follow the time evolution of wildfire smoke from near the point of emission to locations 2–3.5 hours downwind. In nine flights we made repeated transects of wildfire plumes at varying downwind distances and could thereby follow the plume's time evolution. On average there was little change in dilution-normalized aerosol mass concentration as a function of downwind distance. This consistency hides a dynamic system in which primary aerosol particles are evaporating and secondary ones condensing. Organic aerosol is oxidized as a result. On all transect more than 90 % of aerosol is organic. In freshly emitted smoke aerosol, NH4+ is approximately equivalent to NO3−. After two hours of daytime aging, NH4+ increased and is approximately equivalent to the sum of Cl−, SO42− and NO3−. Particle size increased with downwind distance causing particles to be more efficient scatters. Averaged over nine flights, mass scattering efficiency increased in ~ two hours by 56 % and in one fight doubled. Coagulation and material transport from small to large particles are discussed as mechanisms for increasing particle size. As absorption remained nearly constant with age the time evolution of single scatter albedo was controlled by age-dependent scattering. Near-fire aerosol had a single scatter albedo (SSA) of 0.8–0.9. After one to two hours of aging SSAs were typically 0.9 and greater. Assuming global-average surface and atmospheric conditions, the observed age-dependence in SSA would change the direct radiative effect of a wildfire plume from near zero near the fire to a cooling effect downwind.
52 citations
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TL;DR: In this paper, the authors investigated the air quality in the Kathmandu valley during the pre-monsoon season 2015 and found that PM 2.5 concentrations ranged from 30 to 207 µ g'm −3, which exceeded the World Health Organization 24'hguideline by factors of 1.2 to 8.3.
Abstract: . The Kathmandu Valley in Nepal is a bowl-shaped urban basin that experiences severe air pollution that poses health risks to its 3.5 million inhabitants.
As part of the Nepal Ambient Monitoring and Source Testing Experiment
(NAMaSTE), ambient air quality in the Kathmandu Valley was investigated from
11 to 24 April 2015, during the pre-monsoon season. Ambient concentrations
of fine and coarse particulate matter (PM 2.5 and PM 10 ,
respectively), online PM 1 , inorganic trace gases ( NH3 , HNO3 ,
SO2 , and HCl), and carbon-containing gases ( CO2 , CO, CH4 , and
93 non-methane volatile organic compounds; NMVOCs) were quantified at a
semi-urban location near the center of the valley. Concentrations and ratios
of NMVOC indicated origins primarily from poorly maintained vehicle
emissions, biomass burning, and solvent/gasoline evaporation. During those
2 weeks, daily average PM 2.5 concentrations ranged from 30 to 207 µ g m −3 , which exceeded the World Health Organization 24 h
guideline by factors of 1.2 to 8.3. On average, the non-water mass of
PM 2.5 was composed of organic matter (48 %), elemental carbon
(13 %), sulfate (16 %), nitrate (4 %), ammonium (9 %), chloride
(2 %), calcium (1 %), magnesium (0.05 %), and potassium (1 %). Large
diurnal variability in temperature and relative humidity drove corresponding
variability in aerosol liquid water content, the gas–aerosol phase
partitioning of NH3 , HNO3 , and HCl, and aerosol solution pH. The
observed levels of gas-phase halogens suggest that multiphase
halogen-radical chemistry involving both Cl and Br impacted regional air
quality. To gain insight into the origins of organic carbon (OC), molecular
markers for primary and secondary sources were quantified. Levoglucosan
(averaging 1230±1154 ng m −3 ), 1,3,5-triphenylbenzene ( 0.8±0.6 ng m −3 ), cholesterol ( 2.9±6.6 ng m −3 ), stigmastanol (1.0
±0.8 ng m −3 ), and cis-pinonic acid ( 4.5±1.9 ng m −3 )
indicate contributions from biomass burning, garbage burning, food cooking,
cow dung burning, and monoterpene secondary organic aerosol, respectively.
Drawing on source profiles developed in NAMaSTE, chemical mass balance (CMB)
source apportionment modeling was used to estimate contributions to OC from
major primary sources including garbage burning ( 18±5 %), biomass
burning ( 17±10 %) inclusive of open burning and biomass-fueled
cooking stoves, and internal-combustion (gasoline and diesel) engines ( 18±9 %). Model sensitivity tests with newly developed source profiles
indicated contributions from biomass burning within a factor of 2 of
previous estimates but greater contributions from garbage burning
(up to three times), indicating large potential impacts of garbage burning
on regional air quality and the need for further evaluation of this source.
Contributions of secondary organic carbon (SOC) to PM 2.5 OC included
those originating from anthropogenic precursors such as naphthalene ( 10±4 %) and methylnaphthalene ( 0.3±0.1 %) and biogenic
precursors for monoterpenes ( 0.13±0.07 %) and sesquiterpenes ( 5±2 %). An average of 25 % of the PM 2.5 OC was unapportioned,
indicating the presence of additional sources (e.g., evaporative and/or
industrial emissions such as brick kilns, food cooking, and other types of
SOC) and/or underestimation of the contributions from the identified source
types. The source apportionment results indicate that anthropogenic
combustion sources (including biomass burning, garbage burning, and
fossil fuel combustion) were the greatest contributors to PM 2.5 and, as
such, should be considered primary targets for controlling ambient PM
pollution.
45 citations
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TL;DR: In this article, the authors used positive matrix factorization (PMF) to examine the systematics of nitrogen emissions from 75 stack fires in western US wildfires and found that CO2 is recommended as a marker for Nr emissions.
Abstract: . Reactive nitrogen ( Nr , defined as all nitrogen-containing
compounds except for N2 and N2O ) is one of the most important
classes of compounds emitted from wildfire, as Nr impacts both
atmospheric oxidation processes and particle formation chemistry. In
addition, several Nr compounds can contribute to health impacts from
wildfires. Understanding the impacts of wildfire on the atmosphere requires
a thorough description of Nr emissions. Total reactive nitrogen was
measured by catalytic conversion to NO and detection by NO– O3
chemiluminescence together with individual Nr species during a series
of laboratory fires of fuels characteristic of western US wildfires,
conducted as part of the FIREX Fire Lab 2016 study. Data from 75 stack fires
were analyzed to examine the systematics of nitrogen emissions. The measured
Nr ∕ total-carbon ratios averaged 0.37 % for fuels characteristic of
western North America, and these gas-phase emissions were compared with fuel
and residue N∕C ratios and mass to estimate that a mean ( ±SD )
of 0.68 ( ±0.14 ) of fuel nitrogen was emitted as N2 and N2O .
The Nr detected as speciated individual compounds included the following: nitric
oxide (NO), nitrogen dioxide ( NO2 ), nitrous acid (HONO), isocyanic acid
(HNCO), hydrogen cyanide (HCN), ammonia ( NH3 ), and 44 nitrogen-containing volatile organic compounds (NVOCs). The sum of these
measured individual Nr compounds averaged 84.8 ( ±9.8 ) %
relative to the total Nr , and much of the 15.2 % “unaccounted”
Nr is expected to be particle-bound species, not included in this
analysis. A number of key species, e.g., HNCO, HCN, and HONO, were confirmed not to
correlate with only flaming or with only smoldering combustion when using
modified combustion efficiency, MCE = CO 2 / ( CO + CO 2 ) , as a
rough indicator. However, the systematic variations in the abundance of
these species relative to other nitrogen-containing species were
successfully modeled using positive matrix factorization (PMF). Three
distinct factors were found for the emissions from combined coniferous
fuels: a combustion factor (Comb-N) (800–1200 ∘C ) with emissions
of the inorganic compounds NO, NO2 , and HONO, and a minor contribution
from organic nitro compounds (R- NO2 ); a high-temperature pyrolysis
factor (HT-N) (500–800 ∘C ) with emissions of HNCO, HCN, and
nitriles; and a low-temperature pyrolysis factor (LT-N) ( ∘C ) with mostly ammonia and NVOCs. The temperature ranges
specified are based on known combustion and pyrolysis chemistry
considerations. The mix of emissions in the PMF factors from chaparral fuels
(manzanita and chamise) had a slightly different composition: the Comb-N
factor was also mostly NO, with small amounts of HNCO, HONO, and NH3 ;
the HT-N factor was dominated by NO2 and had HONO, HCN, and HNCO; and
the LT-N factor was mostly NH3 with a slight amount of NO contributing.
In both cases, the Comb-N factor correlated best with CO2
emission, while the HT-N factors from coniferous fuels correlated closely
with the high-temperature VOC factors recently reported by Sekimoto et al. (2018), and the LT-N had some correspondence to the LT-VOC factors. As a
consequence, CO2 is recommended as a marker for combustion Nr
emissions, HCN is recommended as a marker for HT-N emissions, and the family
NH3 ∕ particle ammonium is recommended as a marker for LT-N emissions.
41 citations
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TL;DR: This article evaluated the smoke from wild and prescribed fires using downwind measurements that include both inert tracers to test production and transport and reactive species to detect reactive species in the smoke and evaluate the smoke.
Abstract: Evaluating our understanding of smoke from wild and prescribed fires can benefit from downwind measurements that include both inert tracers to test production and transport and reactive species to ...
34 citations
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TL;DR: The results show that garbage burning emissions could increase PM2.5 concentrations by nearly 30% in India and Nepal, and result in ~300,000 premature deaths from chronic obstructive pulmonary disease in the two countries.
Abstract: Increasing air pollution in South Asia has serious consequences for air quality and human/ecosystem health within the region. South Asia, including India and Nepal, suffers from severe air pollutio...
28 citations
01 Dec 2020
2 citations