The annual DHL relay race in Fælledparken, Copenhagen, is generating significant air pollution, primarily due to the numerous charcoal grills used at the event. Independent measurements reveal that ultrafine particle levels in the air during the race are three times higher than those recorded on Copenhagen’s busiest roads during rush hour. This concerning level of pollution is attributed to the widespread use of charcoal grills at the tents set up along the route. Runners participating in the DHL relay race not only experience the communal spirit of the event but are also exposed to a substantial amount of smoke. The high concentration of ultrafine particles poses potential health risks to participants and attendees.