Ar hyn o bryd amcangyfrifir bod ansawdd aer gwael yn cyfrannu at ddisgwyliad oes is a marwolaeth, sy'n cyfateb â rhwng 1,000 a 1,400 o farwolaethau yng Nghymru bob blwyddyn. Mae Sefydliad Iechyd y Byd (WHO) yn nodi mai llygredd aer yw'r risg iechyd amgylcheddol unigol mwyaf, yn fyd-eang.
It is currently estimated poor air quality contributes to a reduced life expectancy and death, tallying an equivalent of between 1,000 and 1,400 mortalities in Wales each year. The World Health Organisation (WHO) states air pollution as the single largest environmental health risk, globally.