Advanced Air Purification Systems at the Age of COVID-19

新冠肺炎疫情导致对声称可以去除或灭活病毒和其他生物气雾剂的空气净化设备的需求增加。这些设备中应用的技术不仅包括高效过滤器等高效过滤技术，还包括UV、紫外光催化氧化、等离子体和电离器等电子空气净化(EAC)系统。大多数EAC会产生自由基和臭氧等氧化剂，它们可以使生物气溶胶失活，并氧化空气中的气体和蒸气。此外，自新冠肺炎疫情爆发以来，建议将频繁的表面消毒和手部卫生作为一种预防措施，以减少病毒传播；这些做法已被大多数建筑采用，无论是哪种类型。-最近的一项研究评估了政府建议/批准用于对抗冠状病毒的清洁和消毒产品，以防止挥发性有机化合物(VOCs)排放。他们总共确定了399种VOCs；其中127种VOCs被归类为潜在危险化合物。这种室内VOCs的新来源加剧了室内空气质量(IAQ)，并迫切需要进行基础研究，以更好地了解VOCs控制措施及其对建筑设计和运营的影响。PCO是一种很有前途的去除室内环境中VOCs的技术。紫外光存在下的二氧化钛基光催化剂PCO在控制室内环境VOCs方面得到了广泛的研究。理论上，碳氢化合物VOCs完全PCO的最终产物应该是CO2和H2O。然而，反应物的部分氧化会产生副产物，比母体化合物对人体健康的危害更大。大量的参数可能会影响PCO系统的性能和副产品的产生，这些都没有得到系统的研究。另一方面，PCO过程中产生的副产物可能会与原始污染物竞争吸附在光催化剂的表面，从而对光催化剂的去除速度产生不利影响。建议的研究工作旨在解决与PCO技术相关的一些关键缺点，使其成为在不断变化的世界中应用于暖通空调系统的更成熟和更可靠的选择。主要目标是开发一个全面的副产物生成预测模型，并提出VOC混合物的降解途径。所开发的模型将使用实验数据进行验证。这种模型可用于提高PCO系统的去除效率，并将副产品的产生对健康的风险降至最低。准确定位PCO过程中VOCs的降解机理也将有利于设计出更高效、反应动力学更强、耐久性更好的光催化剂。此外，随着更多用于去除气相空气污染物的空气净化设备进入市场，开发一种评估其性能的程序和开发设计工具将是至关重要的。

The COVID-19 pandemic has caused increased demand for air cleaning devices that claim to remove or inactivate virus and other bioaerosols. The technologies applied in such devices are not only high efficiency filtration like HEPA filters, but also electronic air cleaning (EAC) systems like UV, UV-photocatalytic oxidation, plasma and ionizers. Most EACs generate oxidizing agents like radicals and ozone, which can deactivate bioaerosols and oxidize gases and vapors in the air. Moreover, since the start of the COVID-19 pandemic, frequent surface disinfection and hand sanitization have been recommended as a preventative measure to reduce viral transmission; these practices have been adopted by most buildings regardless of the type.  A recent study evaluated cleaning and disinfecting products that government-recommended/approved to use against the coronavirus, for volatile organic compounds (VOCs) emissions. They identified a total 399 VOCs; among them 127 VOCs are classified as potentially hazardous compounds.  This new source of indoor VOCs has exacerbated the indoor air quality (IAQ), and created an urgent need for fundamental studies for better understanding of VOCs control measures and their effects on building design and operations. PCO is a promising technology for removing VOCs from indoor environment. PCO with TiO2 based photocatalyst in the presence of UV light has been widely studied for controlling indoor environment VOCs. Theoretically, the final products of complete PCO for hydrocarbon VOCs should be CO2 and H2O. However, partial oxidation of reactants generates by-products that can be more harmful to human health than the parent compound. A large number of parameters  can impact the performance of PCO system and by-product generation which have not been systematically investigated. On the other hand, the by-products generated during PCO might compete with the original pollutant for adsorption on the photocatalyst's surface and adversely affect the removal rate. The proposed research work aims to address some of the key shortcomings associated with PCO technology so as to make it a more mature and reliable option applied in HVAC system in the changing world. The primary goal is to develop a comprehensive predictive model for generation of by-products and to propose degradation pathways for VOC mixtures. The developed model will be validated using the experimental data. Such model can be employed to boost the removal efficiency of PCO systems and minimize the health risks posed by generation of by-products. Accurately mapping the degradation mechanism of VOCs during PCO would also be beneficial to designing more efficient photocatalysts with enhanced reaction kinetics and superior durability. Furthermore, as more air cleaning devices for the removal of gas-phase air pollutants enter the market, it would be essential to develop a procedure to evaluate their performance and develop design tools.