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1. Flame-Free Candles Are Not Pollution-Free: Scented Wax Melts as a Significant Source of Atmospheric Nanoparticles

   https://doi.org/10.1021/acs.estlett.4c00986  

   Patra, Satya S; Jiang, Jinglin; Liu, Jianghui; Steiner, Gerhard; Jung, Nusrat; Boor, Brandon E (February 2025, Environmental Science & Technology Letters)

   Scented wax melts are being popularized as a safer, nontoxic alternative to traditional candles and incense for indoor aromatherapy. We performed field measurements in a residential test house to investigate atmospheric nanoparticle formation from scented wax melt use. We employed a high-resolution particle size magnifier-scanning mobility particle sizer (PSMPS) and a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) for real-time monitoring of indoor atmospheric nanoparticle size distributions and terpene mixing ratios, respectively. Our findings reveal that terpenes released from scented wax melts react with indoor atmospheric ozone (O3) to initiate new particle formation (NPF) events, resulting in significant indoor atmospheric nanoparticle concentrations (>10^6 cm^–3) comparable to those emitted by combustion-based scented candles, gas stoves, diesel engines, and natural gas engines. We show that scented wax melt-initiated NPF events can result in significant respiratory exposures, with nanoparticle respiratory tract deposited dose rates similar to those determined for combustion-based sources. Our results challenge the perception of scented wax melts as a safer alternative to combustion-based aromatherapy, highlighting the need for further research on the toxicological properties of the newly formed nanoparticles to better understand their environmental health implications. 

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2. Rapid Nucleation and Growth of Indoor Atmospheric Nanocluster Aerosol during the Use of Scented Volatile Chemical Products in Residential Buildings

   https://doi.org/10.1021/acsestair.4c00118  

   Patra, Satya S; Liu, Jianghui; Jiang, Jinglin; Ding, Xiaosu; Huang, Chunxu; Keech, Connor; Steiner, Gerhard; Stevens, Philip S; Jung, Nusrat; Boor, Brandon E (September 2024, ACS ES&T Air)

   Scented volatile chemical products (sVCPs) are frequently used indoors. We conducted field measurements in a residential building to investigate new particle formation (NPF) from sVCP emissions. State-of-the-art instrumentation was used for real-time monitoring of indoor atmospheric nanocluster aerosol (NCA; 1–3 nm particles) size distributions and terpene mixing ratios. We integrated our NCA measurements with a comprehensive material balance model to analyze sVCP-nucleated indoor NCA dynamics. Our results reveal that sVCPs significantly increase indoor terpene mixing ratios (10–1,000 ppb), exceeding those in outdoor forested environments. The emitted terpenes react with indoor atmospheric O3 and initiate indoor NPF, resulting in nucleation rates as high as ∼10^5 cm^–3 s–1 and condensational growth rates up to 300 nm h^–1; these are orders of magnitude higher than those reported during outdoor NPF events. Notably, high particle nucleation rates significantly increase indoor atmospheric NCA concentrations (10^5–10^8 cm^–3), and high growth rates drive their survival and growth to sizes that efficiently reach the deepest regions of the human respiratory system. We found sVCP-nucleated NCA to cause respiratory exposures and dose rates comparable to or exceeding those from primary aerosol sources such as gas stoves and diesel engines, highlighting their significant impact on indoor atmospheric environments. 

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3. Siloxane Emissions and Exposures during the Use of Hair Care Products in Buildings

   https://doi.org/10.1021/acs.est.3c05156  

   Jiang, Jinglin; Ding, Xiaosu; Patra, Satya S.; Cross, Jordan N.; Huang, Chunxu; Kumar, Vinay; Price, Paige; Reidy, Emily K.; Tasoglou, Antonios; Huber, Heinz; et al (November 2023, Environmental Science & Technology)

   Cyclic volatile methyl siloxanes (cVMS) are ubiquitous in hair care products (HCPs). cVMS emissions from HCPs are of concern, given the potential adverse impact of siloxanes on the environment and human health. To characterize cVMS emissions and exposures during the use of HCPs, realistic hair care experiments were conducted in a residential building. Siloxane-based HCPs were tested using common hair styling techniques, including straightening, curling, waving, and oiling. VOC concentrations were measured via proton-transfer-reaction time-of-flight mass spectrometry. HCP use drove rapid changes in the chemical composition of the indoor atmosphere. cVMS dominated VOC emissions from HCP use, and decamethylcyclopentasiloxane (D5) contributed the most to cVMS emissions. cVMS emission factors (EFs) during hair care routines ranged from 110–1500 mg/person and were influenced by HCP type, styling tools, operation temperatures, and hair length. The high temperature of styling tools and the high surface area of hair enhanced VOC emissions. Increasing the hair straightener temperature from room temperature to 210 °C increased cVMS EFs by 50–310%. Elevated indoor cVMS concentrations can result in substantial indoor-to-outdoor transport of cVMS via ventilation (0.4–6 tons D5/year in the U.S.); thus, hair care routines may augment the abundance of cVMS in the outdoor atmosphere. 

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4. PTR-TOF-MS eddy covariance measurements of isoprene and monoterpene fluxes from an eastern Amazonian rainforest

   https://doi.org/10.5194/acp-20-7179-2020  

   Sarkar, Chinmoy; Guenther, Alex B.; Park, Jeong-Hoo; Seco, Roger; Alves, Eliane; Batalha, Sarah; Santana, Raoni; Kim, Saewung; Smith, James; Tóta, Julio; et al (January 2020, Atmospheric Chemistry and Physics)

   null (Ed.)

   Abstract. Biogenic volatile organic compounds (BVOCs) are important components of the atmosphere due to their contribution to atmospheric chemistry and biogeochemical cycles. Tropical forests are the largest source of the dominant BVOC emissions (e.g. isoprene and monoterpenes). In this study, we report isoprene and total monoterpene flux measurements with a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) using the eddy covariance (EC) method at the Tapajós National Forest (2.857∘ S, 54.959∘ W), a primary rainforest in eastern Amazonia. Measurements were carried out from 1 to 16 June 2014, during the wet-to-dry transition season. During the measurement period, the measured daytime (06:00–18:00 LT) average isoprene mixing ratios and fluxes were 1.15±0.60 ppb and 0.55±0.71 mg C m−2 h−1, respectively, whereas the measured daytime average total monoterpene mixing ratios and fluxes were 0.14±0.10 ppb and 0.20±0.25 mg C m−2 h−1, respectively. Midday (10:00–14:00 LT) average isoprene and total monoterpene mixing ratios were 1.70±0.49 and 0.24±0.05 ppb, respectively, whereas midday average isoprene and monoterpene fluxes were 1.24±0.68 and 0.46±0.22 mg C m−2 h−1, respectively. Isoprene and total monoterpene emissions in Tapajós were correlated with ambient temperature and solar radiation. Significant correlation with sensible heat flux, SHF (r2=0.77), was also observed. Measured isoprene and monoterpene fluxes were strongly correlated with each other (r2=0.93). The MEGAN2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) model could simulate most of the observed diurnal variations (r2=0.7 to 0.8) but declined a little later in the evening for both isoprene and total monoterpene fluxes. The results also demonstrate the importance of site-specific vegetation emission factors (EFs) for accurately simulating BVOC fluxes in regional and global BVOC emission models. 

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5. Emerging investigator series: primary emissions, ozone reactivity, and byproduct emissions from building insulation materials

   https://doi.org/10.1039/c9em00024k  

   Chin, Kyle; Laguerre, Aurelie; Ramasubramanian, Pradeep; Pleshakov, David; Stephens, Brent; Gall, Elliott T. (August 2019, Environmental Science: Processes & Impacts)

   Building insulation materials can affect indoor air by (i) releasing primary volatile organic compounds (VOCs) from building enclosure cavities to the interior space, (ii) mitigating exposure to outdoor pollutants through reactive deposition (of oxidants, e.g. , ozone) or filtration (of particles) in infiltration air, and (iii) generating secondary VOCs and other gas-phase byproducts resulting from oxidant reactions. This study reports primary VOC emission fluxes, ozone (O 3 ) reaction probabilities ( γ ), and O 3 reaction byproduct yields for eight common, commercially available insulation materials. Fluxes of primary VOCs from the materials, measured in a continuous flow reactor using proton transfer reaction-time of flight-mass spectrometry, ranged from 3 (polystyrene with thermal backing) to 61 (cellulose) μmol m −2 h −1 (with total VOC mass emission rates estimated to be between ∼0.3 and ∼3.3 mg m −2 h −1 ). Major primary VOC fluxes from cellulose were tentatively identified as compounds likely associated with cellulose chemical and thermal decomposition products. Ozone-material γ ranged from ∼1 × 10 −6 to ∼30 × 10 −6 . Polystyrene with thermal backing and polyisocyanurate had the lowest γ , while cellulose and fiberglass had the highest. In the presence of O 3 , total observed volatile byproduct yields ranged from 0.25 (polystyrene) to 0.85 (recycled denim) moles of VOCs produced per mole of O 3 consumed, or equivalent to secondary fluxes that range from 0.71 (polystyrene) to 10 (recycled denim) μmol m −2 h −1 . Major emitted products in the presence of O 3 were generally different from primary emissions and were characterized by yields of aldehydes and acetone. This work provides new data that can be used to evaluate and eventually model the impact of “hidden” materials ( i.e. , those present inside wall cavities) on indoor air quality. The data may also guide building enclosure material selection, especially for buildings in areas of high outdoor O 3 . 

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