SARS-CoV-2在室内和室外的长距离和短距离空气传播的风险评估
Risk assessment for long and short range airborne transmission of SARS-CoV-2, indoors and outdoors
摘要：
我们需要采取预防措施以减少感染，以对抗COVID-19大流行，并为可能出现的地方病阶段做好准备。目前的预防性疫苗对预防疾病非常有效，但由于病毒进化导致免疫逃逸增加，因此失去了减少病毒传播的能力。因此，长期积极的公共卫生政策必须与现有的非药物干预措施（NPI）补充疫苗接种，以降低公共场所的病毒传播风险。在这里，我们重新审视空气传播风险的定量评估，考虑渐近限制，大大简化了其表达。我们表明，气溶胶传播的风险是三个因素的产物：一个生物因素，取决于病毒株，流体动力学因素定义为吸入和呼出的空气之间的病毒颗粒的浓度比，和口罩过滤因子。在室内和室外，对风险的短期贡献与通过气流和对流（室内）或风（室外）呼出的气溶胶的湍流扩散有关。我们的实验表明，空气中的液滴和CO $_2$分子呈现相同的分散。因此，无论房间容积、新鲜空气流速和占用率如何，都可以使用CO $_2$浓度定量测量稀释因子和风险。我们表明，分散锥导致病毒颗粒的浓度，因此，短距离传播的风险，与感染者的平方距离和流速成反比。气溶胶化标准作为一个中间的结果，比较斯托克斯弛豫时间的拉格朗日时间尺度，可能会发现应用广泛的一类气溶胶传播的病原体和污染物。
英文摘要：
Preventive measures to reduce infection are needed to combat the COVID-19 pandemic and prepare for a possible endemic phase. Current prophylactic vaccines are highly effective to prevent disease but lose their ability to reduce viral transmission as viral evolution leads to increasing immune escape. Long term proactive public health policies must therefore complement vaccination with available nonpharmaceutical interventions (NPI) aiming to reduce the viral transmission risk in public spaces. Here, we revisit the quantitative assessment of airborne transmission risk, considering asymptotic limits that considerably simplify its expression. We show that the aerosol transmission risk is the product of three factors: a biological factor that depends on the viral strain, a hydrodynamical factor defined as the ratio of concentration in viral particles between inhaled and exhaled air, and a face mask filtering factor. The short range contribution to the risk, both present indoors and outdoors, is related to the turbulent dispersion of exhaled aerosols by air drafts and by convection (indoor), or by the wind (outdoors). We show experimentally that airborne droplets and CO$_2$ molecules present the same dispersion. As a consequence, the dilution factor, and therefore the risk, can be measured quantitatively using the CO$_2$ concentration, regardless of the room volume, the flow rate of fresh air and the occupancy. We show that the dispersion cone leads to a concentration in viral particles, and therefore a short range transmission risk, inversely proportional to the squared distance to an infected person and to the flow velocity. The aerosolization criterion derived as an intermediate result, which compares the Stokes relaxation time to the Lagrangian time scale, may find application for a broad class of aerosol-borne pathogens and pollutants.
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