Model Evaluation of Secondary Chemistry due to Disinfection of Indoor Air with Germicidal Ultraviolet Lamps

Air disinfection using germicidal ultraviolet light (GUV) has received increasing attention during the COVID-19 pandemic. GUV uses UVC lamps to inactivate microorganisms, but it also initiates photochemistry in air. However, GUV’s indoor-air-quality impact has not been investigated in detail. Here, we model the chemistry initiated by GUV at 254 (“GUV254”) or 222 nm (“GUV222”) in a typical indoor setting for different ventilation levels. Our analysis shows that GUV254, usually installed in the upper room, can significantly photolyze O3, generating OH radicals that oxidize indoor volatile organic compounds (VOCs) into more oxidized VOCs. Secondary organic aerosol (SOA) is also formed as a VOC-oxidation product. GUV254-induced SOA formation is of the order of 0.1–1 μg/m3 for the cases studied here. GUV222 (described by some as harmless to humans and thus applicable for the whole room) with the same effective virus-removal rate makes a smaller indoor-air-quality impact at mid-to-high ventilation rates. This is mainly because of the lower UV irradiance needed and also less efficient OH-generating O3 photolysis than GUV254. GUV222 has a higher impact than GUV254 under poor ventilation due to a small but significant photochemical production of O3 at 222 nm, which does not occur with GUV254

Comparison of demographic and clinical characteristics between non MDR^a DR-TB^b (n = 47) and MDR-TB (n = 9) among 56 DR-TB patients diagnosed in the Children's Hospital of Chongqing Medical University during 2008–2013 using logistic regression models.

<p>Comparison of demographic and clinical characteristics between non MDR<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151303#t004fn001" target="_blank">^a</a> DR-TB<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151303#t003fn002" target="_blank">^b</a> (n = 47) and MDR-TB (n = 9) among 56 DR-TB patients diagnosed in the Children's Hospital of Chongqing Medical University during 2008–2013 using logistic regression models.</p

Comparison of demographic and clinical characteristics between pansensitive (n = 140) and MDR-TB^a (n = 9) diagnosed in the Children's Hospital of Chongqing Medical University during 2008–2013 (n = 149) using logistic regression models.

<p>Comparison of demographic and clinical characteristics between pansensitive (n = 140) and MDR-TB<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151303#t003fn001" target="_blank">^a</a> (n = 9) diagnosed in the Children's Hospital of Chongqing Medical University during 2008–2013 (n = 149) using logistic regression models.</p

Comparison of frequency distribution of age (Panel a), sex (Panel b) and disease site (Panel c) between the 196 culture-confirmed cases diagnosed in the Children’s Hospital of Chongqing Medical University (CHCMU) during 2008–2013 that were included in the study sample and the 164 culture-confirmed cases diagnosed at CHCMU during the same time period that were not included in the study sample.

<p>Chi-square test showed that there was no significant differences in age, sex and disease site frequency distribution between the included and excluded cases (p>0.05).</p

Drug susceptibility to first-line anti-tuberculosis drugs among 196 culture-confirmed pediatric tuberculosis cases diagnosed in the Children's Hospital of Chongqing Medical University during 2008–2013.

<p>Drug susceptibility to first-line anti-tuberculosis drugs among 196 culture-confirmed pediatric tuberculosis cases diagnosed in the Children's Hospital of Chongqing Medical University during 2008–2013.</p

Facile Pyrolyzed N‑Doped Binder Network for Stable Si Anodes

Although nanoengineering provides improved stability of Si-based nanostructures, a facile and efficacious method to directly use raw Si practices is still absent. Herein, we report a pyrolyzed N-doped binder network to improve the cycling stability of raw Si particles. Such an N-doped binder network is formed at a conformal pyrolysis condition of the electrode binder using polyacrylonitrile and provides a tight encapsulation of the Si particles with significantly improved cycling stability. In contrast to the single Si particles that pulverize and lose the total capacity at the 20th cycle, the discharge capacity could be retained ∼1700 mA h g^–1 at the 100th cycle for the Si particles imbedded in the pyrolyzed N-doped binder network. Our results demonstrate that such a facile remedy could significantly improve the cycling stability of raw Si particles for high-energy-density lithium-ion batteries

Frequency distribution of drug-resistant patterns observed among all 196 culture-confirmed tuberculosis patients diagnosed in the Children's Hospital of Chongqing Medical University during 2008–2013.

<p>INH-isoniazid, RIF-rifampicin, EMB-ethambutol, STR-streptomycin.</p

Li₂O‑Reinforced Cu Nanoclusters as Porous Structure for Dendrite-Free and Long-Lifespan Lithium Metal Anode

A nanostructured protective structure, pillared by the copper nanoclusters and in situ filled with lithium oxide in the interspace, is constructed to efficiently improve the cyclic stability and lifetime of lithium metal electrodes. The porous structure of copper nanoclusters enables high specific surface area, locally reduced current density, and dendrite suppressing, while the filled lithium oxide leads to the structural stability and largely extends the electrode lifespan. As a result of the synergetic protection of the proposed structure, lithium metal could be fully discharged with efficiency ∼97% for more than 150 cycles in corrosive alkyl carbonate electrolytes, without dendrite formation. This approach opens a novel route to improve the cycling stability of lithium metal electrodes with the appropriate protective structure

Effects of 222 nm Germicidal Ultraviolet Light on Aerosol and VOC Formation from Limonene

Since the 1930s, germicidal ultraviolet (GUV) irradiation has been used indoors to prevent the transmission of airborne diseases, such as tuberculosis and measles. Recently, it has received renewed attention due to the COVID-19 pandemic. While GUV radiation has been shown to be effective in inactivating airborne bacteria and viruses, few studies on the impact of GUV on indoor air quality have been published. In this work, we evaluate the effects of GUV222 (GUV at 222 nm) on the chemistry of a common indoor volatile organic compound (VOC), limonene. We found that the production of O3 by the GUV222 lamps caused the formation of particulate matter (PM) and oxygenated volatile organic compounds (VOCs). We also found that the chemistry proceeds through the ozonolysis of limonene as well as the reaction with secondary OH, and that the presence of GUV light led to observable but small perturbations to this chemistry. Understanding the effects of GUV222 on indoor air quality is important in evaluating the safety of these devices

Model Evaluation of New Techniques for Maintaining High-NO Conditions in Oxidation Flow Reactors for the Study of OH-Initiated Atmospheric Chemistry

Oxidation flow reactors (OFRs) efficiently produce OH radicals using low-pressure Hg-lamp emissions at λ = 254 nm (OFR254) or both λ = 185 and 254 nm (OFR185). OFRs under most conditions are limited to studying low-NO chemistry (where RO₂ + HO₂ dominates RO₂ fate), even though substantial amounts of initial NO may be injected. This is due to very fast NO oxidation by high concentrations of OH, HO₂, and O₃. In this study, we model new techniques for maintaining high-NO conditions in OFRs, that is, continuous NO addition along the length of the reactor in OFR185 (OFR185-cNO), recently proposed injection of N₂O at the entrance of the reactor in OFR254 (OFR254-iN₂O), and an extension of that idea to OFR185 (OFR185-iN₂O). For these techniques, we evaluate (1) fraction of conditions dominated by RO₂ + NO while avoiding significant nontropospheric photolysis and (2) fraction of conditions where reactions of precursors with OH dominate over unwanted reactions with NO₃. OFR185-iN₂O is the most practical for general high-NO experiments because it represents the best compromise between experimental complexity and performance upon proper usage. Short lamp distances are recommended for OFR185-iN₂O to ensure a relatively uniform radiation field. OFR185-iN₂O with low O₂ or using Hg lamps with higher 185 nm-to-254 nm ratio can improve performance. OFR185-iN₂O experiments should generally be conducted at higher relative humidity, higher UV, lower concentration of non-NO_<i>y</i> external OH reactants, and percent-level N₂O. OFR185-cNO and OFR185-iN₂O at optimal NO precursor injection rate (∼2 ppb/s) or concentration (∼3%) would have satisfactory performance in typical field studies where ambient air is oxidized. Exposure estimation equations are provided to aid experimental planning. This work enables improved high-NO OFR experimental design and interpretation