Karachi has been ranked as one of the most polluted cities in the world
Syrian air defences were activated in a similar way over west Damascus
Concentrations of lung-damaging ozone hit a record high in China in June
Pictures on social media showed participants braved heat and unhealthy air quality in some places to spotlight yoga
Patients to continue to come in until end of May
Reaction Engines unlocks advanced propulsion that could change the future of air and space travel
France and the UN have repeatedly called for the opening of aid corridors to alleviate the humanitarian crisis
Pakistan is 'one of few countries who do not monitor air quality'