First Insights Into The Main Air Pollutant Loads At The Petrohan Forest Site: One Year Of Measurements

Abstract

Air pollution can still impact forest ecosystems' health, although pollution levels are far from those of the 80s, and the significant improvement in emissions could suggest different hypotheses. Recent studies are focused on drought, disease, and pests, but air pollution still plays a role and could have a synergistic effect on forest health. Some air pollutants, like ground-level ozone, could have a real impact on forests. Ozone is considered a dangerous regional air pollutant for plants because of its high phytotoxicity, resulting from its strong oxidising power and direct effects on various physiological processes, thereby increasing susceptibility to pests and diseases. According to the European Environment Agency (EEA), in 2022, 62% of the total forest area exceeded critical levels for forest protection in the EEA member countries. Although nitrogen oxides are the least phytotoxic among ozone and sulphur dioxide, they play an important role as local pollutants in atmospheric chemistry and have a strong impact on vegetation. They act as ground-level ozone precursors and have a fertilising effect by promoting vegetation’s growth, but can also have a negative effect by causing eutrophication of the ecosystems. Sulphur dioxide is a regional pollutant, primarily emitted by the industrial and energy sectors. Effective policy measures have significantly reduced SO 2 emissions in recent decades, addressing the problem of acidification. Even though there are some places where SO 2 emissions have shifted in recent years. SO 2 can negatively impact ecosystems, altering soil chemical composition or directly affecting plants via stomata. The European Union sets standards to protect vegetation from ambient air pollution, including critical levels for ozone, nitrogen oxides, and sulphur dioxide, through the Ambient Air Quality Directive. The current study provides insights into the atmospheric chemical conditions under which beech and spruce forests in the region grow and examines whether the critical levels for vegetation protection were exceeded during the first year of air-pollutant measurements at the Petrohan Forest site. The Cairsens microsensors were used to measure ground-level ozone, sulphur and nitrogen dioxide. The SO 2 levels remained consistently below the measuring equipment's detection limit, underscoring the absence of industrial activity in the area. The monthly ground-level ozone concentrations during the vegetation period are relatively low (63.41 µg/m 3 ), while NO 2 concentrations are elevated. The diurnal profile analysis reveals morning ozone titration and a single afternoon NO 2 peak, driven by transit traffic and mountain-valley circulation. Seasonal dynamics indicate that July is the most critical month; ozone values regularly exceed the 80 µg/m 3 threshold, which creates conditions for phytotoxic stress and the accumulation of harmful doses, as indicated by the AOT40 index, during the active growth period.