LONDON — New research from the London School of Economics has found that students exposed to polluted air before taking their exams end up receiving lower scores.

For the study, 2,418 students in the Greater London urban area were tested taking a total of 11,443 exams over a period of several weeks. Researchers found that a one unit increase of PM 10 levels indoors resulted in a 0.055 to 2.230 percentage point decrease in student test scores.

The study explained that particle pollution is classified as "inhalable coarse particles" or PM 10, and "fine particles," or PM 2.5, on the basis of their size.

Particles larger than 2.5 micrometers and smaller than 10 micrometers in diameter are referred to as PM, 10 while particles that are 2.5 micrometers or smaller in diameter are called PM 2.5.

The study tested indoor air pollution levels in exam rooms and found PM 10 levels above 75 micrograms per cubic meter. This was able to reduce a student's test score by 3.41 percentage points.

The World Health Organization's limit for PM 10 is 50 micrograms per cubic meter.

Sefi Roth, a researcher from the London School of Economics who was involved with the study, told the Times of London that students should limit their outdoor activity on polluted days and try to take the less polluted route to school, the Irish Post reports.

A separate study examining the impact of PM 2.5 on Israeli students also found a significant decline in student performance.
The study found that a one standard deviation increase of PM 2.5 resulted in students' performance declining by 0.93 percentage points.

The researchers also showed that 10 additional units of PM 2.5 is associated with a 1.5 percentage point decline.