Bo Yuan

High-altitude terrain may intersect the upper atmospheric boundary layer and exhibit distinct environmental dynamics. We investigated the anthropogenic pollutants polychlorinated alkanes (PCAs, also known as chlorinated paraffins) in surface soils along a transect from the La Paz-El Alto metropolitan area in Bolivia (3200-4100 masl) to the upper slopes of Mount Chacaltaya (>5200 masl), around 16 km away. Concentrations of PCAs in urban soils (750-5,230 ng/g organic carbon [OC]) decreased exponentially with increasing distance from the urban boundary, declining to ∼150 ng/g OC at elevations below 4,700 masl. Beyond 4,700 masl concentrations increased again, reaching levels comparable to those in the urban area, 1,670-4,300 ng/g OC, above 5,000 masl. Given that pollutant concentrations typically decline with distance from their source, this altitudinal trend, together with a pronounced shift in PCA forensic fingerprints near 4,700 masl, strongly suggests contributions from sources beyond the local metropolitan area. Carbon and nitrogen isotope signatures in organic carbon further support long-range transport as a source, consistent with previous modeling and observations that the upper slopes of Mount Chacaltaya predominantly receive air masses and organic carbon from distant regions via transport in the free troposphere. Our observation that pollutant levels in high-altitude areas are comparable to those in the metropolis of 1.8-million inhabitants underscores the efficiency of long-range atmospheric transport.

Reliable quantification of polychlorinated alkanes (PCAs) remains a major challenge, hindering environmental research across diverse matrices. Each sample can contain over 500 homologue groups, collectively producing >1000 m/z ratios that require interference checks. High-resolution mass spectrometry methods vary in ionization signals and data formats and require specialized algorithms for quantification. CPxplorer streamlines data processing through the integration of three modules: (1) CPions generates target ion sets and isotopic thresholds for compound identification into the next module; (2) Skyline performs instrument-independent data integration, interference evaluation, and homologue profiling; and (3) CPquant deconvolves homologues and reports concentrations using reference standards and homologue profiles from Skyline. Evaluation of the workflow with NIST-SRM-2585 dust and ERM-CE100 fish tissue material yielded comparable results across raw data formats from different instruments. Further applications of CPxplorer across diverse matrices, including indoor dust, organic films, silicone wrist bands, and food samples, demonstrated the usefulness in biological and environmental monitoring. Compared to existing tools limited to qualitative detection, CPxplorer enables quantitative outputs, reduces processing time, and expands functionality to PCA-like substances (e.g., BCAs) and PCA degradation products (e.g., OH-PCAs). CPxplorer reduces learning barriers, empowers users to quantify PCAs across various analytical instruments, and contributes to generating comparable results in the field.