METROLOGY AND CLIMATE CHANGE

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Climate change is one of the greatest challenges of our time because it affects all life on Earth. To understand it and make informed decisions, we need reliable and comparable measurements — from air temperature and sea level to the concentration of greenhouse gases.

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Climate data must be accurate, comparable, and homogeneous. Changes of only a few tenths of a degree in average temperature, a few percent in atmospheric water vapour, or a sea-level rise of just a few millimetres per year make an enormous difference in predicting future atmospheric conditions. This is why metrology is the foundation of meteorology and its branch, climatology.

(Visual 1: Meteorological station with measuring instruments / Source: Croatian Meteorological and Hydrological Service – DHMZ)

Across the world, calibrated instruments are used to measure temperature, relative humidity, air pressure, wind speed and direction, and precipitation. Satellites and oceanographic buoys measure sea level, salinity, and ocean temperature by depth, while laboratories analyse concentrations of carbon dioxide, methane, ozone, and various harmful atmospheric pollutants. Only if the instruments are accurately calibrated and traceable to international standards can measurement data be compared between countries, continents, and long time periods (e.g., 10 years or more).

(Visual 2: Wind tunnel in a calibration laboratory / Source: DHMZ)

In Croatia, such atmospheric measurements across the entire country are conducted by the Croatian Meteorological and Hydrological Service (DHMZ), which maintains the national network of meteorological stations and the stations of the National Air Quality Monitoring Network.

Stations of the National Air Quality Monitoring Network measure inorganic compounds (sulphur dioxide (SO₂), hydrogen sulphide (H₂S), nitrogen oxides (NO, NO₂, NOₓ), ammonia (NH₃), carbon monoxide (CO), ozone (O₃), methane (CO/CO₂/CH₄), total gaseous mercury (Hg)), volatile organic compounds (benzene (C₆H₆)), and particulate matter (PM₁₀, PM₂.₅, black carbon). Data from all stations are publicly accessible on the DHMZ website and on the Croatian Air Quality Portal, managed by the Ministry of Environmental Protection and Green Transition.

Ozone exists in both the troposphere (the atmospheric layer from the Earth’s surface up to about 12 km) and the stratosphere (from 12 km to 50 km altitude). While high stratospheric ozone concentrations are desirable — forming a sufficiently thick protective ozone layer — high tropospheric ozone concentrations are not.

Stratospheric ozone is formed through chemical reactions involving UV radiation and oxygen. These reactions occur continuously whenever UV light is present. Substances that damage the ozone layer include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), carbon tetrachloride, methyl chloroform, halons, and others. These substances are inert in the lower atmosphere and were therefore used in refrigerators, aerosol propellants, pesticides, and solvents. However, after the discovery of the ozone hole in the late 20th century, their environmental impact became clear. CFCs and HCFCs were also identified as greenhouse gases. The ozone layer is now on a path to recovery thanks to coordinated global action.

Tropospheric (ground-level) ozone is a greenhouse gas whose elevated concentrations can harm human, animal, and plant health and damage materials. It forms during sunny weather, low humidity, and when air is rich in nitrogen oxides and volatile hydrocarbons (from vehicle exhaust). The problem is most pronounced in large cities with heavy traffic and in regions with strong photochemical activity, such as the Mediterranean.

In the National Air Quality Monitoring Network, ozone is measured at 23 out of 31 stations.

(Visual 3: Air-quality monitoring container, DHMZ, Osijek / Source: DHMZ)

DHMZ also serves as the national measurement standards laboratory (NML) for ozone concentration and gas mixtures. This means it develops and maintains the reference standards for these measurements, performs instrument calibrations, and ensures that data from Croatia are comparable with those from the rest of the world. Without this role, ozone measurements from Zagreb or Split would lack international credibility.

(Visual 4: National standard for ground-level ozone concentration / Source: DHMZ)

Thanks to metrology, we can reliably monitor and compare the changes occurring in our environment and in nature.