Bewildered Moscow residents woke up on Thursday to discover a strange green cloud hovering over the city.
Soon social media soon became flooded with photographs and videos and numerous theories as what the cause of the colourful smog could be.
This video was uploaded to Twitter by Moscow resident @korobkov.
Cars and windows in the city became covered in a green film and some worried whether the cloud could have been the result of a chemical spill.
But responding to panicked phone calls from residents, officials issued assurances that the smog was only the product of tree pollen and some unusual weather.
An official told the Russian news agency Interfax: "High heat, which came to the Moscow region with an intense wind, caused the formation of a large amount of pollen, which, mixing and moving in the air, can form such a cloud."