The northern parts of China are suffering from recurring smog, which reminds us of the severity of a pollution battle that could last for decades before the environment substantially improves.

Smog at moderate and intense levels hit the Beijing-Tianjin-Hebei areas again on Wednesday evening and will last until Saturday, according to national meteorological authorities. Pollution has already hit various areas this month, shrouding the Beijing International Marathon on Oct 19. It will arrive again around Oct 28.

The smog, mostly composed of PM2.5, or particulate matter smaller than 2.5 micrometers in diameter, can affect human lungs and the bloodstream. Once such particles enter the human body, they are not easily discharged. They can cause diseases such as asthma, bronchitis and cardiovascular disorders.

The increased frequency of smog hitting the northern regions has raised an alarm, indicating that the situation could be worsening and prompting measures to ease the severity.

However, even if policymakers and the public join hands to strictly implement its anti-pollution policies, it will take many years for the country to rebuild a clean environment.

Researchers have pinpointed four reasons for the smog, including weather (less wind, since wind helps disperse smog), industrial pollutants, automobile emissions, and coal and straw burning. From a macroeconomic perspective, however, it is but an inevitable result of the country's galloping economic expansion in the past 30 years.

Economic development is not necessarily accompanied by pollution. But in the economic history of the mankind, economic activities very often lead to pollution and environmental degradation. It is happening in China now, and it happened in Western countries decades ago.