COVID 19 - The Hidden Rise in Toxic Air Pollution during the COVID-19 Pandemic: is our response worsening the respiratory burden of particulate matter

最近的研究强调了一个令人担忧的范式，即减少以PM2.5形式存在的法定空气污染的环境浓度，可能会通过增加更有害的超细颗粒（UFP;直径小于100 nm）的浓度而导致空气质量下降。研究表明，PM2.5在抑制UFP数量方面起着至关重要的作用，较大的PM2.5颗粒可以从空气中清除毒性更大的UFP。因此，去除作为UFP汇的PM2.5可能导致环境UFP数量增加，特别是如果UFP排放和气态前体浓度仍然不受控制。随着COVID-19大流行的爆发，地球仪各地的人类活动以前所未有的方式大幅减少，以至于通常测量的主要空气污染物浓度大幅下降。然而，二次污染物（通常与最细的UFP组分相关）的水平已经开始上升。因此，全球人为活动和环境PM2.5的突然下降有可能导致UFP浓度意外和潜在的显著增加以及相关的有害健康影响。如果我们现在无意中在许多人容易受到影响呼吸系统的病毒影响的时候向空气中添加了一种意想不到的心肺污染物，我们就有可能扩大COVID-19的“可接受性窗口”，在这种情况下，增加UFP暴露会加剧先前存在合并症的个体的基础疾病，否则他们可能会被认为是“较低风险”，并加剧病毒对那些已经被认为“处于危险之中”的人的影响。

Recent research has highlighted the concerning paradigm that reducing ambient concentrations of legislated air pollution, in the form of PM2.5, may lead to a decline in air quality by increasing the concentration of more harmful ultrafine particles (UFP; diameter less than 100nm). It has been shown that PM2.5 plays a crucial role in suppression of UFP numbers, with larger PM2.5 particles acting to scavenge the more toxic UFP from the air. Consequently, removal of PM2.5 as a UFP sink may result in enhanced ambient UFP numbers, particularly if UFP emissions and gaseous precursor concentrations remain unchecked. With the outbreak of the COVID-19 pandemic, anthropogenic activity around the globe has decreased in a vast and unprecedented manner, to such an extent that concentrations of commonly measured primary air pollutants have decreased dramatically. However, levels of secondary pollutants (which often correlate with finest UFP fractions) have already begun to rise. It follows that this sudden, global drop in anthropogenic activity and ambient PM2.5 has the potential to drive an unexpected and potentially significant increase in UFP concentrations and associated detrimental health effects. If we are now inadvertently adding an unlooked-for cardio-respiratory pollutant into the air at a time when many are vulnerable to a virus that impacts the respiratory system, we risk widening the COVID-19 'window of vulnerability', where increased UFP exposure acts to exacerbate underlying conditions for individuals with pre-existing co-morbidities, who may otherwise be considered 'lower risk', and worsen the impact of the virus for those already considered as 'at risk'.