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1. 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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2. 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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3. Chemical composition and size of individual indoor aerosol particles during cooking experiments in wintertime Fairbanks, Alaska, 2022

   https://doi.org/10.18739/a2xp6v566  

   Forshee, Logan; Pratt, Kerri (January 2025, NSF Arctic Data Center)

   The Alaskan Layered Pollution and Chemical Analysis field campaign was conducted in Fairbanks, Alaska from January to February 2022. Individual aerosol particles were measured indoors with particle sizing instrumentation and an aerosol time-of-flight mass spectrometer during cooking experiments inside a residential house (64.850°N, 147.676°W). The goal of this work was to understand the chemical composition and size of individual indoor aerosol particles while cooking experiments were conducted. Here we report indoor aerosol number concentrations, aerosol number mode diameters, average individual aerosol particle mass spectra, and chemically-resolved number fractions during nine cooking experiments. We also report chemically-resolved number fractions with particle diameter. 

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4. Chemistry and Human Exposure Implications of Secondary Organic Aerosol Production from Indoor Terpene Ozonolysis

   https://doi.org/10.1126/sciadv.abj9156  

   Rosales, C.M.F.; Jiang, J.; Lahib, A.; Bottorff, B.P.; Reidy, E.K.; Kumar, V.; Tasoglou, A.; Huber, H.; Dusanter, S.; Tomas, A.; et al (January 2022, Science advances)

   Surface cleaning using commercial disinfectants, which has recently increased during the coronavirus disease 2019 pandemic, can generate secondary indoor pollutants both in gas and aerosol phases. It can also affect indoor air quality and health, especially for workers repeatedly exposed to disinfectants. Here, we cleaned the floor of a mechanically ventilated office room using a commercial cleaner while concurrently measuring gas-phase precursors, oxidants, radicals, secondary oxidation products, and aerosols in real time; these were detected within minutes after cleaner application. During cleaning, indoor monoterpene concentrations exceeded outdoor concentrations by two orders of magnitude, increasing the rate of ozonolysis under low (<10 ppb) ozone levels. High number concentrations of freshly nucleated sub–10-nm particles (≥105 cm−3) resulted in respiratory tract deposited dose rates comparable to or exceeding that of inhalation of vehicle-associated aerosols. 

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5. Indoor–Outdoor Oxidative Potential of PM _2.5 in Wintertime Fairbanks, Alaska: Impact of Air Infiltration and Indoor Activities

   https://doi.org/10.1021/acsestair.3c00067  

   Yang, Yuhan; Battaglia, Michael A; Robinson, Ellis S; DeCarlo, Peter F; Edwards, Kasey C; Fang, Ting; Kapur, Sukriti; Shiraiwa, Manabu; Cesler-Maloney, Meeta; Simpson, William R; et al (March 2024, ACS ES&T Air)

   Bertram, Timothy H (Ed.)

   The indoor air quality of a residential home during winter in Fairbanks, Alaska, was investigated and contrasted with outdoor levels. Twenty-four-hour average indoor and outdoor filter samples were collected from January 17 to February 25, 2022, in a residential area with high outdoor PM2.5 concentrations. The oxidative potential of PM2.5 was determined using the dithiothreitol-depletion assay (OPDTT). For the unoccupied house, the background indoor-to-outdoor (I/O) ratio of mass-normalized OP (OPmDTT), a measure of the intrinsic health- relevant properties of the aerosol, was less than 1 (0.53 ± 0.37), implying a loss of aerosol toxicity as air was transported indoors. This may result from transport and volatility losses driven by the large gradients in temperature (average outdoor temperature of −19°C/average indoor temperature of 21 °C) or relative humidity (average outdoor RH of 78%/average indoor RH of 11%), or both. Various indoor activities, including pellet stove use, simple cooking experiments, incense burning, and mixtures of these activities, were conducted. The experiments produced PM2.5 with a highly variable OPmDTT. PM2.5 from cooking emissions had the lowest OP values, while pellet stove PM2.5 had the highest. Correlations between volume-normalized OPDTT (OPvDTT), relevant to exposure, and indoor PM2.5 mass concentration during experiments were much lower compared to those in outdoor environments. This suggests that mass concentration alone can be a poor indicator of possible adverse effects of various indoor emissions. These findings highlight the importance of considering both the quantity of particles and sources (chemical composition), as health metrics for indoor air quality. 

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