COVID-19 AoT Air Quality Change Report, Chicago

Created by: Chang Zhao

NORC Research Methodologist

2020-05-18

Array of Things is funded by the National Science Foundation

For more information please contact:

Eric Young

NORC Senior External Affairs Manager

young-eric@norc.org

Ned English

NORC Senior Research Methodologist

english-ned@norc.org

Kevin Brown

NORC Vice President in Academic Research Centers

brown-kevin@norc.org

Introduction

This report shows how air quality during the COVID-19 period changes compared to a baseline for the City of Chicago, using AoT Sensor Data. Although air quality varies from community to community within the city, this report focuses on aggregated statistics and daily trends at the city level.

To explore the tool, you could customize 1) the daily statistics of interest, 2) the date range of the baseline period for comparison, 3) the date range in which you expect air quality would change in response to COVID-19 conditions, and 4) the type of data source. The rest of the report will be updated according to your specifications.

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There are two types of data source: (1) Raw version: we keep all raw AoT records unless they are beyond sensor's minimum and maximum limits, such as negative values. (2) 'Cleaned' version: some excluded AoT data points reported air pollutant concentrations above the maximum level of instantaneous concentrations found in the literature (Stern, 1968). In particular, data points where O3 > 1 ppm, H2S > 1 ppm, SO2 > 5 ppm, NO2 > 1 ppm and CO > 100 ppm are considered extremely rare in reality and are removed from the raw dataset for visualization. There is a critical need to discuss with the AoT team to reach resolution about what should count as valid measurements so as to further clean the dataset.

Section 1: Baseline vs. COVID-19

* Because all of the 2020 PM2.5 and PM10 data come from the Ashburn sensor, city-level aggregated estimates for PM2.5 and PM10 are suppressed.

* Because all of the 2020 PM2.5 and PM10 data come from the Ashburn sensor, city-level aggregated estimates for PM2.5 and PM10 are suppressed.

Figure 1 shows trends in air quality over several weeks with the most recent data representing approximately 1-2 days ago-this is how long it takes AoT to publish real-time air quality data. The blue region on the plots represents baseline period, and the red region represents COVID-19 period, for which 2020-03-10 was specified as the default start date (red vertical line) unless otherwise reset by user. It was empirically chosen based on Google's COVID-19 community mobility report, which shows a significant reduction in human activities in IL, likely in response to policies aimed at combating COVID-19 (https://www.google.com/covid19/mobility/). You are encouraged to try different values of the start and end dates, as well as the type of statistics, Figure 1 (and Table 1) will be updated accordingly.

As another reference point, the orange line on the graph indicates the first complete day when Illinois statewide Stay-At-Home Order was in effect for Illinois residents. This order is expected to begin at 5 p.m. 2020-03-21 and continue through May 30.

Section 2: 2019 vs. 2020

We also examine how air quality changes during the COVID-19 period in 2020 compared to the same dates in 2019 (Table 2, Figure 2). Again, you are encouraged to experiment with different values of the input dates and type of statistics, Table 2 and Figure 2 will be updated accordingly.

* Data may be coming from different sensors in the two time periods. PM2.5 and PM10 sensors are only available in Ashburn in 2020, as opposed to multiple communities including Ashburn in 2019. As a result, city-level aggregated estimates for PM2.5 and PM10 are suppressed.

* Data may be coming from different sensors in the two time periods. PM2.5 and PM10 sensors are only available in Ashburn in 2020, as opposed to multiple communities including Ashburn in 2019. As a result, city-level aggregated estimates for PM2.5 and PM10 are suppressed.

Section 3: Air Quality by Neighborhood
Reference:

Stern, A.C., (Ed.). (1968). Air Pollution, 2nd edition. Academic Press, New York.