
http://www.iata.org/publications/economic-briefings/value-of-air-cargo-2016-summary.pdf

https://www.open-britain.co.uk/new_research_trade_deals_with_five_key_countries_could_take_26_years_to_negotiate

https://www.mckinsey.com/mgi/our-research/global-trade-explorer?sector=0ag