Table 1.
Summary statistics.
| Variables | Variable definitions | Obs. | Mean | SD | Min | Max |
|---|---|---|---|---|---|---|
| Panel A: Dependent variables | ||||||
| AQI | Air quality index | 3962 | 68.81 | 35 | 17.25 | 262 |
| SO2 | SO2 concentrations (μg/m3) | 3962 | 11.48 | 8 | 1.745 | 96 |
| PM2.5 | PM2.5 concentrations (μg/m3) | 3962 | 46.2 | 30 | 7.369 | 238 |
| PM10 | PM10 concentrations (μg/m3) | 3962 | 68.31 | 36 | 13.964 | 277 |
| NO2 | NO2 concentrations (μg/m3) | 3962 | 25.59 | 13 | 4.071 | 84 |
| CO | CO concentrations (mg/m3) | 3962 | 0.85 | 0 | 0.205 | 3 |
| O3 | O3 concentrations (μg/m3) | 3962 | 53.45 | 17 | 4.649 | 118 |
| Panel B: Independent variables | ||||||
| Inter-city migrants | The number of Inter-city migrants | 3962 | 153,604 | 201,914 | 2195 | 2,374,810 |
| Intra-city migrants | The number of Intra-city migrants | 3962 | 8,740,000 | 2,798,460 | 709,298 | 16,849,696 |
| Treat_lock | Treat_lock = Event dummy × period dummy. Here event dummy set to 1 if a city adopts lockdown measure during the epidemic, period dummy set to 1 if the time is within the lockdowns. | 3962 | 0.32 | 0 | 0 | 1 |
| Panel C: Control variables | ||||||
| Mintem | Daily maximum temperature (°C) | 3962 | 1.98 | 9 | −24.429 | 25 |
| Maxtem | Daily minimum temperature (°C) | 3962 | 12.83 | 9 | −14.571 | 32 |
| Maxwind | Daily maximum steady wind (Km/h) | 3962 | 19.2 | 5 | 4.111 | 44 |
| Maxgust | Daily maximum gust (Km/h) | 3962 | 18.2 | 14 | 0 | 57 |
| Rain | Rainfall(mm) | 3962 | 1.2 | 2 | 0 | 20 |
| Snow | Snow cover(mm) | 3962 | 0.04 | 0 | 0 | 3 |
Notes: We collected the data presented in Table 1 from official sources from the period of 1 January to 9 April, daily, including: the China National Environment Monitoring Center operated by MEE (http://datacenter.mee.gov.cn/), Baidu Maps (https://qianxi.baidu.com/), local governments-run websites, various media outlets, and Freemeteo (https://freemeteo.cn/). By aggregating and merging these datasets, we obtained a city-week panel of 283 Chinese APL cities, which covers 3962 (283 cities × 14 weeks) observations.