On a May morning in 2012, while hiking up the Himalayas, I saw an ABC – an Atmospheric Brown Cloud – linger in the air. Two Nepali colleagues and myself were on a field expedition, about to reach our research station for air quality monitoring at Gosaikunda (4,300 m.a.s.l.), which we reached after a 3-day walk along steep, narrow and very beautiful trails. The weather was favourable, dry, not too cold and calm. We were looking forward to seeing the sunrise along the white mountain peaks after having slept in a stone hut near the holy lake of Gosaikunda.