The Air Quality lab omits a crucial detail from its third question — "Which city IN THE UNITED STATES had the highest ozone readings?" The OpenAQ data set is worldwide, and measured in two different units. It’s a little frustrating to work through and get the wrong answer because the constraint "in the US" isn’t mentioned.
If you watch the lecture again, at about 0:40 into the lab the problem statement includes this paragraph:
You have been asked to identify the top regions in the US with the highest average Ozone levels ...
More important though – did you learn anything about using Athena to query datasets in S3, or did you already know how to do this?