Precipitation in the arid Central Andean Western Cordillera is strongly sensitive to large‐scale atmospheric circulation patterns which transport moisture from different source regions. As a result, the stable water isotopes of precipitation in this region have been difficult to interpret. We analyzed daily rainfall in the southern Peruvian city of Arequipa for water stable isotopes during the 2019 monsoon season to study sub‐seasonal precipitation dynamics. At 2,300 masl elevation, most rain was sourced from easterly moisture transported over the Altiplano, and was isotopically enriched (δ¹⁸O = −5.2‰), likely due to sub‐cloud evaporation. This was contrary to literature expectations that enriched isotopic values indicate Pacific moisture. During a 2‐week period of northerly moisture transport and intense rainfall, we observed rain stable water isotopes shifted to depleted values (δ¹⁸O = −10.3‰). This study provides new context for interpreting time‐varying and elevation‐varying moisture source influence in the Western Cordillera.

Particulate matter smaller than 10 μm (PM₁₀) is an important air pollutant that adversely affects human health by increasing the risk of respiratory and cardiovascular diseases. Recent studies reported multiple extreme PM₁₀ levels at high altitude Peruvian cities, which resulted from a combination of high emissions and limited atmospheric circulation at high altitude. However, the emission sources of the PM₁₀ still remain unclear. In this study, we collected PM₁₀ samples from four sites (one industrial site, one urban site, and two rural sites) at the city of Arequipa, Peru, during the period of February 2018 to December 2018. To identify the origins of PM₁₀ at each site and the spatial distribution of PM₁₀ emission sources, we analyzed major and trace element concentrations of the PM₁₀. Of the observed daily PM₁₀ concentrations at Arequipa during our sampling period, 91% exceeded the World Health Organization (WHO) 24-h mean PM₁₀ guideline value, suggesting the elevated PM₁₀ strongly affected the air quality at Arequipa. The concentrations of major elements, Na, K, Mg, Ca, Fe, and Al, were high and showed little variation, suggesting that mineral dust was a major component of the PM₁₀ at all the sites. Some trace elements, such as Mn and Mo, originated from the mineral dust, while other trace elements, including Pb, Sr, Cu, Ba, Ni, As and V, were from additional anthropogenic sources. The industrial activities at Rio Seco, the industrial site, contributed to significant Pb, Cu, and possibly Sr emissions. At two rural sites, Tingo Grande and Yarabamba, strong Cu emissions were observed, which were likely associated with mining activities. Ni, V, and As were attributed to fossil fuel combustion emissions, which were strongest at the Avenida Independencia urban site. Elevated Ba and Cu concentrations were also observed at the urban site, which were likely caused by heavy traffic in the city and vehicle brake wear emissions.

This study evaluated concentrations of particulate matter with aerodynamic diameter ≤ 10 µm (PM10) and potentially toxic elements (PTEs) in three urban zones of Ilo, a coastal city in southern Peru, during the cold season (July–October 2022). The cold season is characterised by greater atmospheric stability and a lower mixing layer height, which favours pollutant accumulation and scenarios of higher potential exposure. Three contrasting zones were analysed: commercial (UCZ), industrial (UIZ), and peripheral (UPZ), through daily PM10 sampling and analysis of six PTEs (Al, As, Ba, Cu, Mn, and Zn). The UPZ recorded the highest mean PM10 concentration (23.8 ± 11.6 µg/m ³ ), with 5% of daily records exceeding the World Health Organization (WHO) guideline of 45 µg/m ³ , and the highest concentrations of Cu and As, significantly higher than UIZ and UCZ (p < 0.001 and p = 0.015, respectively). The combined application of environmental indices classified UPZ as heavily contaminated by Cu and As, with extreme enrichment (enrichment factor, EF Cu = 2432; EF As = 2393) and considerable ecological risk (potential ecological risk, PER = 384). Back-trajectory analysis (HYSPLIT) revealed that the highest concentration episodes at UPZ coincided with air masses arriving from continental sectors at 1000 m altitude, including the direction of the local smelter. Health risk assessment identified significant non-carcinogenic risk exclusively at UPZ (hazard index, HI = 7.2), dominated by Cu (89%), while the incremental lifetime carcinogenic risk (ILCR) from As remained at acceptable levels. These findings are applicable to industrialised coastal cities with port, metallurgical, and urban activities in developing countries.