Abstract:
Public warning systems reduce one health risk while potentially creating another. Using daily metropolitan city-level data from South Korea (2015–2019) and the staggered rollout of real-time Emergency Disaster Texts (EDT), I show that particulate matter (PM) warnings increase influenza incidence — but only once delivered through high-salience mobile channels. The mechanism is warning-induced indoor congregation. Post-warning flu incidence rises significantly after EDT implementation. The effect is absent in the pre-EDT period, peaks 25–40 days after an alert, and is consistent with secondary transmission chains rather than a single incubation cycle. Online search data confirm rapid substitution toward commercial indoor venues, with behavioral reversion within two days. A brief congregation episode seeds a prolonged epidemiological arc. Effects are concentrated among school-aged children. Falsification tests show no effect on unrelated conditions, isolating a contact-based transmission response driven by signal salience rather than pollution severity. Coupling high-salience warnings with indoor hygiene guidance could mitigate these costs — a design principle applicable to any institution using simultaneous high-salience signals to coordinate protective behavior.


Keywords: Air pollution; Behavioral response; Information policy; Influenza; Alert

JEL Codes: D83, Q53, I18, I12