To explore the effects of air pollution around the world, and the measures that are being taken to try and tackle the issue, HuffPost has launched an in-depth series called Killer Air, combining original reporting from 13 of its international editions.

The project launched on 23 January and more than 30 stories have been published so far in eight languages, by HuffPost journalists in the US, UK, Mexico, Canada, France, Quebec, Brazil, Italy, Spain, Greece, South Africa, Germany and India.

The topic was chosen during a HuffPost summit that brought together the editors-in-chief of the organisation's global editions to identify what topics they could work more closely on that would be of interest to a broader audience but that also have local relevance.

Louise Roug, international director of HuffPost, said the goal of the project was two-fold: to make people more aware of an issue that can often seem invisible, and to show how air pollution disproportionally affects minorities and people living below the poverty line.

"It's not just about social inequality within a country but also globally. If you are in Germany and you have the luxury to think about how to make the city bike-friendly, that's a privileged position to be in, so maybe it's interesting for people in Germany to read about other communities in India, where people don't have the luxury to get away from pollution."

The stories published as part of Killer Air include a piece on how air pollution is affecting a homeless family in Delhi, where pollution recently reached record highs; a report from a low-income housing project in Orlando, Florida, about the impact of car exhaust and fumes on the residents' health; and a look at how Berlin is moving away from cars and building bicycle superhighways and protected lanes.

During the reporting process, HuffPost also reached out to the mayors of New York, London, Paris, Rome, Madrid, Cape Town, Johannesburg, Houston and Montréal, to give them a chance to talk about how they were tackling this global issue at an urban level, and published their op-eds as part of the project.

While the reporting was primarily text-based, some of the pieces included visual elements, such as a graphic on what air pollution does to people's bodies, that was also turned into an Instagram story. The Orlando report included a video about a female resident in the Griffin Park housing project in Florida who suffered from severe respiratory problems, and it was also shared by HuffPost on Facebook.

Meetings were held regularly to coordinate the reporting and discuss which pieces were relevant, however each editor was able to choose the aspects of air pollution they wanted to focus on in their coverage, and tell those stories in their own style.

"We discussed when would be the best time to publish the stories and it became quite obvious it had to be around winter time because for most of the editions that's when the problem is the greatest," Roug added, although it wasn't mandatory for each edition to go live with the project on 23 January, and some chose to do it a few days later.

"There will be cross-collaboration or cross-posting between the editions, for example between our Quebec and France edition, or Mexico and Spain, which are more connected culturally and linguistically. But it's not like everything has to be shared by everyone or that the US somehow decides what happens, so in that way it's quite a decentralised approach.

"It's not like the US is somehow the centre of things, the US is only one centre among many," Roug explained the approach to international coverage at HuffPost.

It was important to enable each newsroom to approach the reporting in the way they thought suited their audiences most, Roug said.

Some of the editions chose to lean more towards solution-oriented reporting and highlight some of the positive steps their countries had taken to combat air pollution, depending also on the public debate in that region.

"There's a different approach to storytelling in all these countries, so sometimes when we translate a piece, it's also about contextualising it to better explain some aspects.

"Maybe the way to tell stories is more argumentative in France, more 'just the facts, ma'am' in America, or more polemic in Britain, for example.

"Some markets are also much more visual in terms of distribution, and all these things go hand in hand, so it was very important for us not to have a cookie-cutter approach to this and say 'because it's done in this way in the US this is how it should be everywhere else'."

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