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纳米）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颗粒可以清除空气中毒性更强的UFP。因此，去除PM2.5作为UFP汇可能会导致环境UFP数量增加，特别是在UFP排放和气态前体浓度不受控制的情况下。随着COVID-19大流行的爆发，全球人为活动以前所未有的方式大幅减少，以至于通常测量的初级空气污染物浓度急剧下降。然而，二次污染物（通常与最细的UFP组分有关）的水平已经开始上升。由此可见，全球人为活动和环境PM2.5的突然下降有可能导致UFP浓度意想不到且可能显著增加，并产生相关的有害健康影响。在许多人容易受到影响呼吸系统的病毒的影响之际，如果我们现在无意中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“脆弱性窗口期”，增加UFP暴露会加剧已有合合性疾病的个人的潜在疾病，否则这些人可能被认为是“风险较低”，并加剧病毒对那些已经被认为是“风险较高”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'.