Concerns over Delhi's annual (and increasingly worse) air pollution problem usually focus on stubble burning - the burning of farm wastes - in the neighbouring states of Punjab and Haryana. However, data suggests that while this contributes to the problem it is not the main cause. In Punjab, where most of such incidents have taken place, the air quality is "moderate". In Delhi it oscillates between "very poor" and "severe". In fact, the contribution of stubble burning to Delhi's pollution was only 16 per cent on Monday, according to monitoring agency SAFAR.