ABSTRACT

Emissions from traffic over the past few decades have become a significant source of air pollution. Among the pollutants emitted are nitrogen oxides (NO_x), 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 (Pinus halepensis) 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 δ¹⁵N and more negative δ¹³C values compared to those at a rural control site. This is likely due to the incorporation of ¹⁵N-enriched NO_x and ¹³C-depleted CO₂ from traffic pollution. Sampled top-soil also exhibited the δ¹⁵N trend. Our results constitute the first known application of dendrogeochemistry to atmospheric pollution monitoring in Malta.

摘要

在过去的几十年中，交通排放已成为空气污染的重要来源。排放的污染物中包括氮氧化物（NO _x），氮氧化物的暴露可能对公共健康有害。最近的研究表明，树木年轮和树叶中的氮（N）稳定同位素比表达了其主要氮源的指纹，使其适合用于生物监测。在这项研究中，我们已将此替代品应用于阿勒颇松（松halepensis）距马耳他最繁忙的道路之一有3个距离，而马耳他是一个交通拥堵严重的国家。我们的结果表明，在1980-2018年期间，在任何调查地点，树木年轮中氮和有机碳（C）的稳定同位素比率均没有变化。然而，在树木的年轮和枝叶上都有明显的统计学上显着的空间趋势。路边和过渡部位表现出更积极的δ ¹⁵ N和多个负δ ¹³相比，这些在农村对照部位C值。这可能是由于掺入了¹⁵种富含N的NO _x和¹³种贫C的CO ₂所致。采样的表层土壤也表现出δ¹⁵ N趋势。我们的结果构成了树状地球化学在马耳他大气污染监测中的第一个已知应用。