A preliminary study into the use of tree-ring and foliar geochemistry as bio-indicators for vehicular NO pollution in Malta.

Emissions from traffic over the past few decades have become a significant source of air pollution. Among the pollutants emitted are nitrogen oxides (NO), exposure to which can be detrimental to public health. Recent studies have shown that nitrogen (N) stable isotope ratios in tree-rings and foliage express a fingerprint of their major N source, making them appropriate for bio-monitoring purposes. In this study, we have applied this proxy to Aleppo pines () at three distances from one of the busiest roads in Malta, a country known to suffer from intense traffic pollution. Our results showed that N and organic carbon (C) stable isotope ratios in tree-rings do not vary over the period 1980-2018 at any of the investigated sites; however, statistically significant spatial trends were apparent in both tree-rings and foliage. The roadside and transitional sites exhibited more positive N and more negative C values compared to those at a rural control site. This is likely due to the incorporation of N-enriched NO and C-depleted CO from traffic pollution. Sampled top-soil also exhibited the N trend. Our results constitute the first known application of dendrogeochemistry to atmospheric pollution monitoring in Malta.