The COVID-19 pandemic made it critical to limit the spread of the disease by enforcing human isolation, restricting travel and reducing social activities. Dramatic improvements to air quality, especially NO₂, have often characterised places under COVID-19 restrictions. Air pollution measurements in Sydney in April 2019 and during the lockdown period in April 2020 show reduced daily averaged NO₂ concentrations: 8.52 ± 1.92 and 7.85 ± 2.92 ppb, though not significantly so (p₁~0.15) and PM_2.5 8.91 ± 4.94 and 7.95 ± 2.64 µg m⁻³, again a non-significant difference (p₁~0.18). Satellite imagery suggests changes that parallel those at ground level, but the column densities averaged over space and time, in false-colour, are more dramatic. Changed human mobility could be traced in increasing times spent at home, assessed from Google Mobility Reports and mirrored in decreased traffic flow on a major road, suggesting compliance with the restrictions. Electricity demand for the State of New South Wales was low under lockdown in early April 2020, but it recovered rapidly. Analysis of the uses of search terms: bushfires, air quality, haze and air pollution using Google Trends showed strong links between bushfires and pollution-related terms. The smoke from bushfires in late 2019 may well have added to the general impression of improved air quality during lockdown, despite only modest changes in the ground level measurements. This gives hints that successful regulation of air quality requires maintaining a delicate balance between our social perceptions and the physical reality.

中文翻译：

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COVID-19期间悉尼空气污染的细微变化或令人震惊的感知

COVID-19大流行使得通过加强人与外界隔离，限制旅行和减少社交活动来限制疾病的传播至关重要。空气质量（尤其是NO _{2）的显着}改善通常是COVID-19限制下的场所特征。空气污染测量在悉尼2019年4月，并在四月锁定期间2020显示减少每日平均NO _2个浓度：8.52±1.92和7.85±2.92 ppb的，虽然不是显著如此（p ₁〜0.15）和PM _2.5 8.91±4.94和7.95±2.64 µg m ^-3，再次差异不显着（p ₁〜0.18）。卫星图像显示的变化与地面水平的变化平行，但假时色随时间和空间平均的柱密度更为显着。根据Google Mobility Reports的评估，人类出行的变化可以追溯到在家里花费的时间增加，并反映出主要道路上的交通流量减少，这表明遵守了这些限制。在2020年4月上旬的锁定下，新南威尔士州的电力需求较低，但很快恢复了。使用Google趋势分析搜索词的用途：林区大火，空气质量，阴霾和空气污染在丛林大火和与污染相关的术语之间显示出紧密的联系。尽管地面测量值仅发生了适度的变化，但2019年末丛林大火产生的烟雾很可能会给人们在锁定期间改善空气质量的总体印象增色。这表明，成功地调节空气质量需要在我们的社会观念与实际状况之间保持微妙的平衡。