Background

Previous studies described the presence of SARS-CoV-2 in outdoor air particulate matter (PM) in urban areas of northern Italy and USA. The city of Madrid was heavily affected by COVID-19 during March-June 2020. Also, this city usually displays high concentrations of PM under several atmospheric situations. This is mandatory to assess the presence of viral RNA in PM, as an indicator of epidemic recurrence. Our study was aimed at investigating the presence of SARS-CoV-2 RNA in outdoor air samples (on PM10, PM2.5 and PM1).

Methods

six samples of PM10, PM2.5 and PM1 were collected between the May 4^th and 22^nd 2020 in Madrid, on quartz fiber filters by using MCV high volume samplers (30 m³ h⁻¹ flow) with three inlets (Digitel DHA-80) for sampling PM10, PM2.5 and PM1. RNA extraction and amplification was performed according to the protocol recently set by Setti et al., 2020c in Italy. Up to three highly specific molecular marker genes (N1, N2, and RP) were used to test the presence of SARS-CoV-2 RNA.

Results

After RNA extraction and expression measurements of N1, N2 and RP genes from all the collected filters, no presence of SARS-CoV-2 RNA was observed. Control test to exclude false positive results were successfully accomplished.

Conclusions

No presence of SARS-CoV-2 in quartz fiber filters samplers for PM10, PM2.5 and PM1 fractions was observed in our study carried out in Madrid during the month of May 2020. Nevertheless, the absence of viral genomes could be due to different factors including: limited social interactions and economic activities resulting in reduced circulation of the coronavirus, lower daily PM concentration in outdoor air, as well as to meteorological stability and higher temperature that characterize spring season. Further researches should be carried out during the winter, in presence of higher viral circulation and daily PM exceedances.

中文翻译：

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锁定期间马德里户外空气样品不同颗粒物分数中SARS-CoV-2 RNA的测定

背景

先前的研究描述了意大利北部和美国市区的室外空气颗粒物（PM）中是否存在SARS-CoV-2。2020年3月至6月，马德里市受到COVID-19的严重影响。此外，该市通常在几种大气情况下显示高浓度的PM。这对于评估PM中病毒RNA的存在是必不可少的，作为流行病复发的指标。我们的研究旨在调查室外空气样本（在PM10，PM2.5和PM1上）中SARS-CoV-2 RNA的存在。

方法

5月4日之间收集PM10，PM2.5和PM1的六个样品^次和22^次采用MCV高体积取样器（30米2020在马德里，石英纤维过滤器³ ħ ^-1流量）有三个入口（DIGITEL含有DHA 80）采样PM10，PM2.5和PM1。RNA的提取和扩增是根据Setti等，2020c在意大利最近制定的方案进行的。最多使用三个高度特异性的分子标记基因（N1，N2和RP）来测试SARS-CoV-2 RNA的存在。

结果

在从所有收集的滤膜中提取RNA并测定N1，N2和RP基因的表达后，未观察到SARS-CoV-2 RNA的存在。排除假阳性结果的对照测试已成功完成。

结论

2020年5月在马德里进行的研究中，未观察到PM10，PM2.5和PM1组分的石英纤维过滤器采样器中存在SARS-CoV-2。但是，病毒基因组的缺失可能是由于不同这些因素包括：有限的社会互动和经济活动导致冠状病毒的流通减少，室外空气中每日PM浓度降低以及春季季节的气象稳定性和较高温度。在冬季，存在较高的病毒循环和每日PM超标的情况下，应进行进一步的研究。