Ozone episodes shared three high dates in 28 of 30 complete windows positive at both sites near selected US bird surveys in 2005-2019

We tested whether ozone episodes at two nearby sites occurred on the same dates before selected US bird surveys in 2005-2019. We used 797 complete 30-day windows in California, Oregon, New York and Pennsylvania. Both sites had an episode above 70 ppb in 30 windows. In 28 of these windows, the sites shared at least three consecutive high dates. One timing exception had episode starts one day apart; the other had starts eight days apart. Of 73 windows positive at either site, 43 had an episode at only one site. Thus, different episode dates explained little of the lack of a shared episode in these records. At 60 ppb, 163 of 173 both-positive windows shared dates. Complete windows covered only 22.1% of filtered surveys and had warmer survey starts than excluded records. Repeated sites, rare events and selected routes limit inference. Later eastern records had no both-positive windows at 70 ppb. These are finite-sample exposure measures, not causal weather or biological effects. The package gives daily evidence, source hashes, code, all results and independent calendar checks.

ozone · episode timing · bird surveys · exposure measurement · observation bias · calendar agreement