Letter from California, USA

On the morning of 9 September 2020, residents of the San Francisco Bay Area awoke to an eerie orange light filtering through the windows (Fig. 1). Over the next day, post-apocalyptic images of the glowing, ash-filled sky flooded social media and became a global news focus. Air quality sharply decreased to unhealthy levels as ash particles fell to the ground. This alarming event was the result of a dry lightning storm that occurred 3 weeks before. During this storm, more than 12 000 lightning strikes hit California in a single week, causing hundreds of fires, two of which ranked among the three largest in California's recorded history. By mid-September, four fires encircled the Bay Area, creating a belt of 4000-ft thick smoke. At the time of this writing, more than 13 million acres (52 000 km2) and 14 000 structures have burned in the Western United States during the current 2020 fire season. In the context of the concurrent coronavirus disease 2019 (COVID-19) pandemic, thousands have been evacuated, and entire neighbourhoods decimated because of wildfires. However, the respiratory consequences of these fires have yet to be fully realized.