Air we breath in our atmosphere within our planet earth is not static. There is a complicated wind system influenced by various factors, like pressure that moves the air circulating within the globe. Hence, the dusts from a localized volcano eruption leads to massive disruption to international fights. Similarly, when an air pollution occurs in one country, eventually it will be distributed to neighboring countries.
Image of Dust Cloud Dispersion from the 2010 Iceland Volcano Eruption, Source: http://www.rainharvest.co.za
In some places it is an annual routines to generate dust particles from smokes by burning agricultural fields in early February to allow the fields to clear before plants and grasses begin to green in spring, e.g. Kansas, USA
Photo of Controlled Burning of Grass, Source: http://cjonline.com
In recent months, the well known German car manufacturer, i.e. Volkswagen has admitted that its vehicles were equipped with software that was used to cheat on emissions tests in USA. Now has to spend USD 7 billion to buy back its 500,000 diesel cars sold to American who filed the law suit because they were cheated on the car emission conformance to US standard, which obviously passed the German standard.
Unfortunately in some countries, aged school bus is licenced and obviously discharge black smoke willingly and the community accepts the scene without a serious fight, not like Americans.
Perhaps, people think that every country is breathing air from different source with different standard of air quality, similar to public tap water.