Smoke from hazard reduction burns caused 'very poor' air quality in Australia's largest capital city during this morning's peak hour commute. Air quality values reached 'very poor' in parts of eastern and southwest Sydney this morning, which is the second highest category in a six-tier scale. The reduced air quality was due to elevated concentrations of fine airborne pollutants and low visibility, at least some of which was caused by bushfire smoke from hazard reduction burns. On Thursday, the NSW Rural Fire Services website listed numerous active hazard reduction burns to the west and north of Sydney, along with one under-control bushfire near Holsworthy. While these fires were partially to blame for Sydney's hazy start, it was made worse by something called a temperature inversion. Temperature inversions form when relatively cool air sits underneath a layer of warmer, less dense air. The boundary between these two layers of air acts like an invisible barrier and can trap smoke, fog and even noise near the ground. Temperature inversions are most common during the cooler months of the year, when wind is light or non-existent. Unfortunately, this also makes them frequent partners of hazard reduction burns. So, are smoky mornings like this a necessary part of living in Sydney and other towns or cities in Australia, or can they be avoided altogether? Hazard reduction burns, which are also called planned or prescribed burns, are an effective way to reduce bushfire fuel loads. These controlled burns are usually performed outside of the bushfire season and can help make other bushfires easier to manage by reducing their ability to spread, possibly saving properties and lives. One of the downsides to hazard reduction burns is that they commonly occur when winds are light and during temperature inversions. As a result, smoke often lingers and can have adverse impacts on people's health. However, if hazard reduction burns were carried out when the wind was strong enough to disperse the smoke, there would be a greater risk that fires would spread and get out of control. The NSW Rural Fire Service recommends the following steps if a hazard reduction burn is planned for your area: - Keep doors and windows closed to prevent smoke entering homes - Keep outdoor furniture under cover to prevent ember burns - Retract pool covers to prevent ember damage - Remove washing from clotheslines - Ensure pets have a protected area - Vehicles must slow down, keep windows up, turn headlights on - Sightseers must keep away from burns for their own safety - If you have asthma or a lung condition, reduce outdoor activities if smoke levels are high and if shortness of breath or coughing develops, take your reliever medicine or seek medical advice So, while hazard reduction burns are inconvenient in some regards, they can prevent more severe impacts from occuring at other times of the year.