The purpose of this study was to make quantitative connections between changes in social and economic activities in northern California urban areas and related Earth system environmental responses to the COVID-19 pandemic in 2020. We tested the hypothesis that the absence of worker activities during Shelter-in-Place in the San Francisco Bay Area detectably altered the infrared heat flux from parking lots, highways, and large building rooftops, caused primarily by quantitative changes in the reflective properties in these different classes of urban surfaces. The Landsat satellite's thermal infrared (TIR) sensor imagery for surface temperature (ST) was quantified for all the large urban features in the Bay Area that have flat (impervious) surfaces, such parking lots, wide roadways, and rooftops. These large impervious surface features in the five-county Bay Area were first delineated and classified using sub-meter aerial imagery from the National Agriculture Imagery Program (NAIP). We then compared Landsat ST data acquired on (or near) the same dates from the three previous years (2017–2019) for all these contiguous impervious surfaces. Results showed that all the large parking lots, roadway corridors, and industrial/commercial rooftops across the entire Bay Area urban landscape were detected by Landsat ST time series as significantly cooler (by 5^o C to 8^o C) during the unprecedented Shelter-in-Place period of mid-March to late-May of 2020, compared to same months of the three previous years. The explanation for this region-wide cooling pattern in 2020 that was best supported by both remote sensing and ground-based data sets was that relatively low atmospheric aerosol lower (PM_2.5) concentrations from mid-March to late May of 2020 resulted in weaker temperature inversions over the Bay Area, higher diurnal surface mixing, and lowered urban surface temperatures, compared to the three previous years.

本研究的目的是在北加州城市地区的社会和经济活动变化与 2020 年 COVID-19 大流行的相关地球系统环境响应之间建立定量联系。我们检验了这样一个假设，即在避难所期间没有工人活动-旧金山湾区的就地可检测地改变了停车场、高速公路和大型建筑物屋顶的红外热通量，这主要是由这些不同类别的城市表面的反射特性的定量变化引起的。Landsat 卫星的地表温度 (ST) 热红外 (TIR) 传感器图像针对湾区具有平坦（不透水）表面的所有大型城市特征进行了量化，例如停车场、宽阔的道路和屋顶。五县湾区的这些大型不透水表面特征首先使用国家农业影像计划 (NAIP) 的亚米航空影像进行描绘和分类。然后，我们比较了所有这些连续不透水表面在前三年（2017-2019 年）相同日期（或附近）获取的 Landsat ST 数据。结果表明，Landsat ST 时间序列检测到整个湾区城市景观中的所有大型停车场、道路走廊和工业/商业屋顶都明显变冷（5^o C 至 8 ^o C）在 2020 年 3 月中旬至 5 月下旬史无前例的就地避难期间，与前三年的相同月份相比。遥感和地面数据集对 2020 年这种全区域降温模式的最好解释是，从 2020 年 3 月中旬到 5 月下旬，大气气溶胶较低 (PM 2.5) 浓度相对较低，导致_气温较低与前三年相比，湾区的逆温、更高的昼夜表面混合和更低的城市表面温度。