Acid rain that fell on Seoul, Gyeonggi Province and Jeju last year had stronger acidity than in 2004.

The National Institute of Environmental Research said Monday that an analysis of 32 nationwide spots found Ganghwa Island off the west coast showed the strongest acidity of 4.1.

Seoul and its two suburbs of Ansan and Pocheon were second with 4.4, followed by Incheon and Chuncheon with 4.5.

Among the 32 areas studied, acidity in eleven places including Seoul, Gyeonggi Province and Jeju Island last year was more intense than in 2004.

Average rain acidity was 4.8 nationwide last year, the same as in 2004 but higher than in 2003.

Rainfall with acidity of 5.6 or lower is considered acid rain. That with acidity of under five is considered relatively strong acid rain.