Northeast's air pollution to subside

Burning of dry crops to blame for heavy smog in grain growing areas

The burning of crop stubble and unfavorable meteorological conditions are to blame for the heavy haze that has recently blanketed most of Northeast China, one of the country's key grain areas, according to the National Joint Research Center for Tackling Key Problems in Air Pollution Control.

Despite the practice of burning crop stubble being illegal, many farmers believe this method to be the most traditional and efficient for this time of year.

The smog in the Beijing-Tianjin-Hebei province area has been attributed to the burning of crop stubble and a surge in the operation of smokestack industries and heavy-duty diesel trucks, it said.

Heavy air pollution started to envelop Northeast China on Oct 22, and by Tuesday, 11 cities across the region had seen their hourly PM2.5 particulate matter level surpass 150 micrograms per cubic meter, according to the center.

Harbin and Suihua in Heilongjiang province even experienced an hourly PM2.5 concentration of 500 mcg/cubic m, it said. At its peak, the hourly density reached 735 mcg/cubic m in the two cities.

China's current national guideline density level for PM2.5 stands at 35 mcg/cubic m.

PM2.5 particulate matter are air pollutant particles with a diameter of 2.5 micrometers or less, that can invade even the smallest airways.

The center said the air pollution in the country's major grain producing region happened mainly because of the burning of crop stubble.

From Saturday to Monday, satellites detected a large number of locations with burning straw, the majority of which are in central Jilin and Liaoning provinces and southern Heilongjiang, it said.

"Due to the burning operation, air pollutants kept accumulating overnight, exacerbating PM2.5 pollution," it said.

It said that following the end of large stubble burning on Sunday and Monday afternoon, the PM2.5 density in Harbin and Suihua increased rapidly to the level of heavy pollution.

The analysis of components in the local PM2.5 pollutant, it said, also shows that stubble burn-off is a major contributor to the haze, as it contains a high proportion of organic matter and potassium ions.

It said low wind speed and a temperature inversion, which prevents the normal churn of the atmosphere, made the dispersal of the air pollutants difficult.

The center said smog may linger in Northeast China until Friday when a cold front arrives, creating favorable meteorological conditions to disperse the air pollutants.

Haze in the Beijing-Tianjin-Hebei area is also expected to come to an end on Friday, thanks to cold air, it said.

Aside from unfavorable meteorological conditions and stubble burn-off in Tianjin, as well as Hebei and Henan provinces, an increase in industrial operations and heavy-duty truck movement are also factors that have made the area suffer, according to the center.

The area's industrial sector reported an increase of roughly 5 percent in electricity consumption in the second half of October from the first half, it said, adding the surge was especially noticeable in the cement and tile sectors.

During the period, it said, the cluster saw the traffic flow of heavy-duty trucks increase by some 14 percent.

houliqiang@chinadaily.com.cn