SHENZHEN intends to reduce concentrated levels of ozone to below 125 micrograms per cubic meter this year in its continued Shenzhen Blue Sky action to improve air quality, Shenzhen Special Zone Daily reported.

    Statistics from the city’s ecology environment bureau showed that Shenzhen reported 33 days in 2019 that exceeded the “healthy” air quality level. They were all caused by higher concentrations of ground-level ozone that, in turn, brought down the city’s air quality ranking among major Chinese cities in 2019.

    The city’s air quality has continued to improve in the past number of years, especially the PM2.5 concentration, which had been reduced to 24 micrograms per cubic meter in 2019, the lowest since 2006 when the city first started monitoring PM2.5 concentration.

    The number of hazy days in 2019 was the lowest of the past three decades, just nine days in total.

    In contrast, however, concentration of ground-level ozone has continued to get worse since 2013. In 2019, the concentration of ozone reached 156 micrograms per cubic meter, approaching the national “unhealthy” standard of 160 micrograms per cubic meter.

    Since 2015, the number of unhealthy days of ozone has surpassed the number of unhealthy days of PM2.5. The city reported 33 days with excessive ozone last year, which lowered its Air Quality Index (AQI) ranking among 168 Chinese cities. Ozone has become a key factor in determining AQI ranking.

    At a recent meeting, the ecology bureau broke down the various tasks and assigned them to different districts to tighten controls of ozone, pledging to ensure 96 percent of days in the year remain within the AQI standard and ozone concentration level remain below 125 micrograms per cubic meter.

    The bureau will set up expert teams to offer diagnostic services to each district and will set up joint teams with related departments to guide ozone pollution treatment in key areas and different districts.

    Ground-level ozone is not directly caused by pollutants, but by a photochemical (sunlight) reaction of pollutants such as nitrogen oxide (NOx), volatile organic compounds (VOCs) and carbon monoxide. High levels of ground-level ozone, as opposed to ozone in the stratosphere, is hazardous to human health.

    A reduction in the ratio of VOCs/NOx to 3 to 1 is the key to curbing ozone pollution, bureau officials said.

    At present, the city’s VOCs emission reduction is far from the theoretical standard and treatment of the source of VOCs has become the primary task.

    (Han Ximin)