Air quality and air pollution sources in a national park. A case study

National parks or biosphere reserves are usually places far away from urban or industrial sites, which facilitates their protection from anthropogenic air pollution. Even though, transport of persistent air pollutants from distant sources may lead to evident effects on the natural protected area.  On the other hand, there are also several examples of national parks located near cities or industrial facilities with significant emissions to the atmosphere, meaning a direct risk to the preservation of ecosystems. In such situations, not only synoptic but also regional effects must be considered to assess the air quality of the site.

This work shows that biosphere reserves and national parks require in situ tools to monitor and detect local and remote air pollution sources which may constitute a threat to flora, fauna, water, and soil. The rising of new industries in surrounding areas, traffic, and remote transport, can change with time and meteorology and so each national park should have a historical database of the air quality in the site. This study reports the research of air pollutants in ‘Las Tablas de Daimiel’ a wetland Mediterranean national park bordered by different cities and new industries in the field of the revalorization of agricultural wastes. Simultaneous data from San Pablo de los Montes, a background station in a rural area isolated from air pollution, are considered as reference.

The work was extended from March 2020 to July 2021, involving the continuous measurement of meteorological data, of surface O₃, NO, NO₂, CO, SO₂ and PM_2.5 inside the park. Twelve campaigns, one week duration, were also performed to sample air in sorbent tubes and analyse volatile organic compounds from anthropogenic sources. The results are discussed considering meteorology, especially wind and speed direction together with the assessment of back-trajectories of remote air masses. The results show that air quality in the park was affected slightly by local and remote air pollution, excepting for the observed high levels of ozone, with a mean value of 71mg.m^-3. Measured mass loadings for the rest of pollutants were low and not in exceedance of the air quality standards. NO_x and SO₂ average concentrations (3.2 and 0.4 mg m^-3, respectively) were below the recommended critical levels for vegetation. The results confirmed the presence of 26 VOCs, potentially coming from anthropogenic sources, mainly aromatics, including BTXs in average concent ration levels below 0.5 mg m^-3. Although a clear diurnal behavior couldn´t  be established, slightly higher concentrations were observed during working days. From the study of local winds and diurnal profiles of VOCs, we could not identify local sources of these pollutants. This indicates that potential nearby sources did not emit significant quantities of these compounds or emissions were sufficiently diluted by dispersion before reaching the park.

Saharan dust events were frequent and contributed to PM_2.5 levels in the site. AOT-40 values above the established threshold for the protection of vegetation were obtained, 25,500 and 19,900 mg m^-3 for 2020 and 2021, respectively.