Senior clinical psychiatrists have called for closer studies on the negative impact of smoggy days on mental health.

Severe pollution has been linked to respiratory problems such as asthma and bronchitis, but few people realize it could trigger "smog depression", said Tian Chenghua, a professor at the Institute for Psychiatric Research at Peking University's No 6 Hospital.

He said it is scientifically proved that some types of depression are closely associated with conditions such as seasonal change and lack of sunlight. These are related to the production of the hormone melatonin, which lightens skin pigmentation.

Beijing Environmental Protection Bureau said on Thursday that the capital saw 58 days of serious pollution in the past year, with residents enduring on average a smoggy day every six to seven days.

PM 2.5 — airborne particulate matter smaller than 2.5 micrometers in diameter — is the major pollutant on most of these days, with the worst pollution occurring in autumn and winter, the bureau said.

"China lacks scientific studies and investigations into how smog relates to human emotions and mental health," Tian said.

"Experts in public health and clinical psychiatry could collaborate on this to better protect physical and mental health amid worsening air pollution."

Pu Chengcheng, a psychiatrist at the hospital, said cases of increased anxiety and feelings of hopelessness caused by weather conditions such as smog, cloudy skies, rain and lack of sunlight are no longer rare.

"On seriously smoggy days, we suggest that patients, particularly those with depression, stay indoors and turn on the lights, even in the daytime," Pu said on Thursday.

Xiao Lei, a university student in Beijing, who has had depression for two years, told China Daily that smoggy weather affects her mood.

"On days of continuous smog, I feel despair. It's as if my life is shrouded in the cloying haze," said the 24-year-old, who was admitted to a hospital after attempting suicide.

Pu said some patients with depression are more sensitive to smoggy weather that can affect their mood.

Xiao added that sunshine can bring her considerable comfort. "I am thinking about leaving Beijing for somewhere with a better environment, particularly the air quality," she said.

Tian said that despite a lack of scientific data in China directly linking mental problems with smog, similar studies on weather and emotional and mental health are not rare internationally. He urged that more attention be focused on the issue.

He cited seasonal affective disorder, also widely known as winter depression and commonplace in northern Europe, as an example.