Background and Purpose: It remains unclear whether acute exposure to fine particulate matter (PM2.5) triggers ischemic stroke events. This study investigated the association of ambient PM2.5 levels with subsequent occurrence of ischemic stroke according to its subtypes, including cardioembolic stroke (CES), large arterial atherosclerosis (LAA), and small vessel occlusion (SVO).
Methods: Using a multicenter hospital-based stroke registry in Fukuoka, Japan, we included 5259 patients with acute ischemic stroke (72.4±12.2 [mean±SD] years, women 39.1%) who had been independent before stroke and were hospitalized within 7 days of onset between April 2011 and March 2016. Time of symptom onset was confirmed, and time-stratified case-crossover analysis was performed to evaluate the association between PM2.5 levels and subsequent occurrence of ischemic stroke. 
Results: Ambient PM2.5 levels at lag 0–1 days was associated with occurrence of ischemic stroke (ambient temperature-adjusted odds ratio [95% confidence interval] per 10 µg/m3: 1.051 [1.010–1.094]). The association of PM2.5 at lag 0–1 days with ischemic stroke was maintained even after adjusting for other air pollutants (nitrogen dioxide, photochemical oxidants, or sulfur dioxide) or influenza epidemics. This association was evident in LAA (1.110 [1.002-1.229]), but not in other stroke subtypes (CES 1.061 [0.971-1.160]; SVO 1.042 [0.966-1.124]). 
Conclusions: These findings suggest that short-term exposure to PM2.5 within 1 day before onset is associated with the subsequent occurrence of ischemic stroke, especially in LAA type.

Short-term exposure to fine particulate matter (PM2.5) and risk of ischemic stroke in Japan