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Nanocluster aerosol (NCA: particles in the size range of 1–3 nm) are a critically important, yet understudied, class of atmospheric aerosol particles. NCA efficiently deposit in the human respiratory system and can translocate to vital organs. Due to their high surface area-to-mass ratios, NCA are associated with a heightened propensity for bioactivity and toxicity. Despite the human health relevance of NCA, little is known regarding the prevalence of NCA in indoor environments where people spend the majority of their time. In this study, we quantify the formation and transformation of indoor atmospheric NCA down to 1 nm via high-resolution online nanoparticle measurements during propane gas cooking in a residential building. We observed a substantial pool of sub-1.5 nm NCA in the indoor atmosphere during cooking periods, with aerosol number concentrations often dominated by the newly formed NCA. Indoor atmospheric NCA emission factors can reach up to ~10^16 NCA/kg-fuel during propane gas cooking and can exceed those for vehicles with gasoline and diesel engines. Such high emissions of combustion-derived indoor NCA can result in substantial NCA respiratory exposures and dose rates for children and adults, significantly exceeding that for outdoor traffic-associated NCA. Combustion-derived indoor NCA undergo unique size-dependent physical transformations, strongly influenced by particle coagulation and condensation of low-volatility cooking vapors. We show that indoor atmospheric NCA need to be measured directly and cannot be predicted using conventional indoor air pollution markers such as PM2.5 mass concentrations and NOx (NO + NO2) mixing ratios. 

Scented wax products, such as candles and wax warmers/melts, are popular fragranced consumer products that are commonly used in residential buildings. As scented wax products are intentionally fragranced to produce pleasant smellscapes for occupants, they may represent an important source of volatile organic compounds (VOCs) to indoor atmospheres. The aim of this study is to evaluate terpene emission factors (EFs) and inhalation intake fractions (iFs) for scented wax products to better understand their impact on indoor chemistry and chemical exposures. Full-scale emission experiments were conducted in the Purdue zEDGE Test House using a variety of scented candles (n = 5) and wax warmers/melts (n = 14) under different outdoor air exchange rates (AERs). Terpene concentrations were measured in real-time using a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS). PTR-TOF-MS measurements revealed that scented candle and wax warmer/melt products emit a variety of monoterpenes (C10H16) and oxygen-containing monoterpenoids (C10H14O, C10H16O, C10H18O, C10H20O), with peak concentrations in the range of 10^−1 to 10^2 ppb. Monoterpene EFs were much greater for scented wax warmers/melts (C10H16 EFs ~ 10^2 mg per g wax consumed) compared to scented candles (C10H16 EFs ~ 10^−1 to 100 mg per g wax consumed). Significant emissions of reactive terpenes from both products, along with nitrogen oxides (NO, NO2) from candles, depleted indoor ozone (O3) concentrations. Terpene iFs were similar between the two products (iFs ~ 10^3 ppm) and increased with decreasing outdoor AER. Terpene iFs during concentration decay periods were similar to, or greater than, iFs during active emission periods for outdoor AERs ≤ 3.0 h^−1. Overall, scented wax warmers/melts were found to release greater quantities of monoterpenes compared to other fragranced consumer products used in the home, including botanical disinfectants, hair care products, air fresheners, and scented sprays. 

Abstract. A new instrument for the measurement of atmosphericnitrous acid (HONO) and hydroxyl radicals (OH) has been developed usinglaser photofragmentation (LP) of HONO at 355 nm after expansion into alow-pressure cell, followed by resonant laser-induced fluorescence (LIF) ofthe resulting OH radical fragment at 308 nm similar to the fluorescenceassay by gas expansion technique (FAGE). The LP/LIF instrument is calibratedby determining the photofragmentation efficiency of HONO andcalibrating the instrument sensitivity for detection of the OH fragment. Inthis method, a known concentration of OH from the photo-dissociation ofwater vapor is titrated with nitric oxide to produce a known concentrationof HONO. Measurement of the concentration of the OH radical fragmentrelative to the concentration of HONO provides a measurement of thephotofragmentation efficiency. The LP/LIF instrument has demonstrated a1σ detection limit for HONO of 9 ppt for a 10 min integration time.Ambient measurements of HONO and OH from a forested environment and an urbansetting are presented along with indoor measurements to demonstrate theperformance of the instrument. 

Abstract. Reactions of the hydroxyl (OH) and peroxy (HO2 and RO2) radicals playa central role in the chemistry of the atmosphere. In addition to controlling the lifetimes ofmany trace gases important to issues of global climate change, OH radical reactionsinitiate the oxidation of volatile organic compounds (VOCs) which can lead to the production ofozone and secondary organic aerosols in the atmosphere. Previous measurements of these radicalsin forest environments characterized by high mixing ratios of isoprene and low mixing ratios ofnitrogen oxides (NOx) (typically less than 1–2 ppb) have shown seriousdiscrepancies with modeled concentrations. These results bring into question our understanding ofthe atmospheric chemistry of isoprene and other biogenic VOCs under low NOxconditions. During the summer of 2015, OH and HO2 radical concentrations, as well as totalOH reactivity, were measured using laser-induced fluorescence–fluorescence assay by gasexpansion (LIF-FAGE) techniques as part of the Indiana Radical Reactivity and Ozone productioN InterComparison (IRRONIC). This campaign took place in a forested area near Indiana University's Bloomington campus which is characterized by high mixing ratios of isoprene (average daily maximum ofapproximately 4 ppb at 28 ∘C) and low mixing ratios of NO (diurnal averageof approximately 170 ppt). Supporting measurements of photolysis rates, VOCs,NOx, and other species were used to constrain a zero-dimensional box model basedon the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism (MCM 3.2),including versions of the Leuven isoprene mechanism (LIM1) for HOx regeneration(RACM2-LIM1 and MCM 3.3.1). Using an OH chemical scavenger technique, the study revealed thepresence of an interference with the LIF-FAGE measurements of OH that increased with bothambient concentrations of ozone and temperature with an average daytime maximum equivalentOH concentration of approximately 5×106 cm−3. Subtraction of theinterference resulted in measured OH concentrations of approximately4×106 cm−3 (average daytime maximum) that were in better agreement with modelpredictions although the models underestimated the measurements in the evening. The addition ofversions of the LIM1 mechanism increased the base RACM2 and MCM 3.2 modeled OH concentrationsby approximately 20 % and 13 %, respectively, with the RACM2-LIM1 mechanism providing thebest agreement with the measured concentrations, predicting maximum daily OH concentrationsto within 30 % of the measured concentrations. Measurements of HO2 concentrationsduring the campaign (approximately a 1×109 cm−3 average daytime maximum)included a fraction of isoprene-based peroxy radicals(HO2*=HO2+αRO2) and were found to agree with modelpredictions to within 10 %–30 %. On average, the measured reactivity was consistent with thatcalculated from measured OH sinks to within 20 %, with modeled oxidation productsaccounting for the missing reactivity, however significant missing reactivity (approximately40 % of the total measured reactivity) was observed on some days.