The provincial Ministry of the Environment has released its annual air quality report for 2013, and though there are some improvements, Hamilton's air quality is still among the worst in the province in some categories.

The report touts overall improvements in air quality across the province over the past 10 years as levels of pollutants and greenhouse gas pollution continue to decrease.

But within that trend, Hamilton's picture is a less positive one for some key pollutants.

Ozone levels in the city have risen sharply in the last 20 years, the report shows. The annual mean for ozone levels downtown rose 62 per cent in the last two decades, and jumped 43 per cent on the Mountain and 41 per cent in the west end, respectively.

In the last 10 years, ozone levels in the west end have risen 23 per cent, which is the highest such jump in the province.

Ozone is a colourless, odourless gas and is a major component of smog. The report calls ozone at the ground level a "significant environmental and health concern."

On the upside, smog days in Hamilton have taken a significant dip in recent years. There were 45 smog days in 2005, compared to just two in 2013, and that was due to forest fire smoke that originated in northwestern Quebec, the ministry says.

The city recorded "very good to good" air quality 90 per cent of the time, the ministry added.

Across the province, annual averages of fine particulate matter were down by 30 per cent. But amid that fall, Hamilton remains an area with high particulate levels.

In fact, downtown Hamilton recorded the highest levels of particulate matter in the province in 2013, the report shows – and those levels have risen since 2004. Particulate matter includes aerosols, smoke, fumes, dust, fly ash and pollen.

Major sources of particulate matter include cars, smelters and industrial facilities. "Due to their small size, they can penetrate deep into the lungs," the report reads.

Downtown Hamilton also had the highest mean concentration of sulphur dioxide in the province, beating out even Sarnia.

On the plus side, nitrogen dioxide is down 37 per cent in the city and carbon monoxide dropped by 50 per cent.

"Cleaner air is important to all people of Ontario and lowers the health risks associated with pollution such as asthma and other respiratory diseases," said ministry spokesperson Lindsay Davidson in a statement.

"The report confirms that actions like the phase-out of coal, emissions trading regulations, industrial air standards and Drive Clean are working and our air quality is improving," she said.

adam.carter@cbc.ca | AdamCarterCBC