SO₂ Initiates the Efficient Conversion of NO₂ 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 SO₂ on the heterogeneous reactions of NO₂ on MgO as a mineral dust surrogate was investigated. The reactivity of MgO to NO₂ is weak, while coexisting SO₂ can increase the uptake coefficients of NO₂ on MgO by 2–3 orders of magnitude. The uptake coefficients of NO₂ on SO₂-aged MgO are independent of NO₂ 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 NO₂ and surface sulfite. In the presence of SO₂, NO₂ 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 SO₂ on the heterogeneous conversion of NO₂ to HONO may have a significant contribution to the unknown sources of HONO observed in polluted areas (for example, in China)

Characterizing PM_2.5 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