Levels of suspended particulate matter in the air rose in fiscal 2001 compared with the previous year, while those of nitrogen dioxide remained almost unchanged, according to an Environment Ministry study released Friday.

The ministry said roughly 66.6 percent of 1,698 general monitoring stations and 47 percent of 423 roadside monitoring stations covered by the study met the government's acceptable levels for SPM. The comparable figures were 84 percent and 66 percent the year before.

SPM is the fine black soot that results from combustion, especially from diesel engines and factories, and is believed to cause respiratory problems.

Officials attributed the unfavorable results to poor wind conditions that could not push away the particles in the atmosphere and yellow sand blown in from mainland China.

Nitrogen dioxide levels were little changed from those of the previous two years, meeting government environmental standards at 99 percent of the general monitoring sites and 79.4 percent of the roadside stations, the survey showed.

Tokyo's roadside air proved the dirtiest in the nation in terms of nitrogen dioxide pollution, with only 37 percent of roadside monitors showing satisfactory figures, followed by Kanagawa Prefecture with 47 percent.

As for SPM, a scant 3 percent of Tokyo's monitors registered acceptable levels, plummeting from 34 percent in fiscal 2000.

Meanwhile, only 0.6 percent of monitoring locations saw levels of photochemical oxidants -- created when sunlight interacts with airborne pollutants such as nitrogen oxides -- meet government standards. This indicates photochemical smog no longer solely affects urban areas.

Sulfur dioxide and carbon monoxide levels, which were also gauged, remained similar to those registered during fiscal 2000, being within government limits in most of the locations.