The 25th Scientific Advisory Committee Meeting of the Acid Deposition Monitoring Network in East Asia (EANET) was held in Vientiane, the capital of the Lao People’s Democratic Republic, from 20 to 22 October 2025. From Mongolia, Mr. E. Battulga, Director-General of the National Agency for Meteorology and Environmental Monitoring (NAMEM), and Dr. Ts. Tsatsral, Director of the Central Laboratory for Environment and Metrology, participated in the meeting.

During the meeting, participants reviewed the implementation progress, achievements, challenges, and lessons learned from the EANET Medium-Term Plan (MTP) 2021–2025, and finalized the draft MTP for 2026–2030, which will be submitted to the Intergovernmental Meeting (IG) for approval. The meeting also discussed the 2025 annual report, the draft Fifth Report on the State of Air Pollution in East Asia, as well as the results of inter-laboratory comparisons, ongoing projects, scientific studies, and research activities among the 13 member countries. In addition, the work plan and budget for 2026 were reviewed and adopted.

Established in 2001, the EANET is an intergovernmental regional cooperation framework aimed at monitoring acid deposition, raising public awareness of acid rain issues, supporting pollution reduction measures, and enhancing cooperation among participating countries. As of 2025, the network comprises 13 member countries.

Acid deposition occurs when substances such as sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) in the atmosphere react with water vapor to form sulphuric acid (H₂SO₄) and nitric acid (HNO₃). The acidity level is expressed by the pH value, which measures the concentration of hydrogen ions in solution. Precipitation with a pH below 5.6 is considered acidic.

Since 1998, NAMEM has been conducting acid deposition monitoring continuously in central Ulaanbaatar and Terelj. Although acid deposition levels in Mongolia are generally low across most regions, urban areas, especially during the heating season, face higher risks due to increased emissions and meteorological conditions.

Long-term observations in Ulaanbaatar show that the average pH of precipitation ranges between 5.5 and 6.8, which is mostly neutral, though during winter months, pH values have occasionally dropped to 4.8–5.2.

Acid deposition can lead to:

• Increased respiratory illnesses among the population

• Loss of soil nutrients and degradation of water and forest ecosystems

• Accelerated corrosion and deterioration of buildings and infrastructure