3 research outputs found
SO<sub>2</sub> Initiates the Efficient Conversion of NO<sub>2</sub> to HONO on MgO Surface
Nitrous acid (HONO) is an important
source of hydroxyl radical
(OH) that determines the fate of many chemically active and climate
relevant trace gases. However, the sources and the formation mechanisms
of HONO remain poorly understood. In this study, the effect of SO<sub>2</sub> on the heterogeneous reactions of NO<sub>2</sub> on MgO as
a mineral dust surrogate was investigated. The reactivity of MgO to
NO<sub>2</sub> is weak, while coexisting SO<sub>2</sub> can increase
the uptake coefficients of NO<sub>2</sub> on MgO by 2–3 orders
of magnitude. The uptake coefficients of NO<sub>2</sub> on SO<sub>2</sub>-aged MgO are independent of NO<sub>2</sub> concentrations
in the range of 20–160 ppbv and relative humidity (0–70%RH).
The reaction mechanism was demonstrated to be a redox reaction between
NO<sub>2</sub> and surface sulfite. In the presence of SO<sub>2</sub>, NO<sub>2</sub> was reduced to nitrite under dry conditions, which
could be further converted to gas-phase HONO in humid conditions.
These results suggest that the reductive effect of SO<sub>2</sub> on
the heterogeneous conversion of NO<sub>2</sub> to HONO may have a
significant contribution to the unknown sources of HONO observed in
polluted areas (for example, in China)
Characterizing PM<sub>2.5</sub> Emissions and Temporal Evolution of Organic Composition from Incense Burning in a California Residence
The chemical composition of incense-generated organic
aerosol in
residential indoor air has received limited attention in Western literature.
In this study, we conducted incense burning experiments in a single-family
California residence during vacancy. We report the chemical composition
of organic fine particulate matter (PM2.5), associated
emission factors (EFs), and gas-particle phase partitioning for indoor
semivolatile organic compounds (SVOCs). Speciated organic PM2.5 measurements were made using two-dimensional gas chromatography
coupled with high-resolution time-of-flight mass spectrometry (GC×GC-HR-ToF-MS)
and semivolatile thermal desorption aerosol gas chromatography (SV-TAG).
Organic PM2.5 EFs ranged from 7 to 31 mg g–1 for burned incense and were largely comprised of polar and oxygenated
species, with high abundance of biomass-burning tracers such as levoglucosan.
Differences in PM2.5 EFs and chemical profiles were observed
in relation to the type of incense burned. Nine indoor SVOCs considered
to originate from sources other than incense combustion were enhanced
during incense events. Time-resolved concentrations of these SVOCs
correlated well with PM2.5 mass (R2 > 0.75), suggesting that low-volatility SVOCs such as
bis(2-ethylhexyl)phthalate
and butyl benzyl phthalate partitioned to incense-generated PM2.5. Both direct emissions and enhanced partitioning of low-volatility
indoor SVOCs to incense-generated PM2.5 can influence inhalation
exposures during and after indoor incense use
High Hydroquinone Emissions from Burning Manzanita
California wildfires are becoming
larger and more frequent because
of climate change and historical fire suppression. The 2017 fire season
was record-breaking in terms of monetary damage, area burned, and
human casualties. In addition, roughly 20 million people were exposed
to dense wildfire smoke for days. Understanding the health impacts
of wildfire smoke requires detailed chemical speciation of smoke produced
from different fuels. This study demonstrates the unique chemical
fingerprint observed in smoke from burning manzanita, a common chaparral
and forest understory shrub found in several ecosystems of California.
Burning manzanita during the FIREX Fire Laboratory experiments emitted
hydroquinone (1,4-dihydroxybenzene with an emission factor of 0.4
g/kg) and two sterol/triterpenoid tracer compounds at levels up to
100 times higher than those of the other common wildland fuels in
California such as pine trees, other shrubs, grasses, and duff. Additionally,
these compounds were detected in Berkeley, CA, from smoke produced
during the October 2017 wildfires in northern California, a region
where manzanita grows. In contrast, the identified fingerprint for
manzanita burning emissions was not observed during prescribed fires
of a mixed conifer forest in California’s Sierra Nevada, indicating
negligible amounts of manzanita were burned. As confirmed by shrub
inventory data collected prior to the burns, small amounts of manzanita
remain after prescribed burning, a low-severity forest management
technique, but larger amounts can occur after recovery from high-severity
events like wildfires. Results from this study show that chemical
signatures in smoke can be traced back to specific fuels like manzanita
and that forest management techniques can be used to limit certain
types of wildfire emissions