Understanding aerosol composition in a tropical inter-Andean valley impacted by agro-industrial and urban emissions

Abstract

Abstract. Agro-industrial areas are frequently affected by various sources of atmospheric pollutants that have a negative impact on public health and ecosystems. However, air quality in these areas is infrequently monitored because of their smaller population compared to large cities, especially in developing countries. The Cauca River valley (CRV) is an agro-industrial region in southwestern Colombia, where a large fraction of the area is devoted to sugarcane and livestock production. The CRV is also affected by road traffic and industrial emissions. This study aims to elucidate the chemical composition of particulate matter fine mode (PM2.5) and to identify the main pollutant sources before source attribution. A sampling campaign was carried out at a representative site in the CRV region, where daily averaged mass concentrations of PM2.5 and the concentrations of water-soluble ions, trace metals, organic and elemental carbon, and various fractions of organic compounds (carbohydrates, n alkanes, and polycyclic aromatic hydrocarbons – PAHs) were measured. The mean PM2.5 was 14.4±4.4 µg m−3, and the most abundant constituent was organic material (52.7 % ± 18.4 %), followed by sulfate (12.7 % ± 2.8 %), and elemental carbon (7.1 % ± 2.5 %), which indicates the presence of secondary aerosol formation and incomplete combustion. Levoglucosan was present in all samples, with a mean concentration of (113.8±147.2 ng m−3), revealing biomass burning as a persistent source. Mass closure using the elemental carbon (EC) tracer method explained 88.4 % on PM2.5, whereas the organic tracer method explained 70.9 % of PM2.5. We attribute this difference to the lack of information of specific organic tracers for some sources, both primary and secondary. Organic material and inorganic ions were the dominant groups of species (79 % of PM2.5). OMprim and OMsec contribute 24.2 % and 28.5 % to PM2.5. Inorganic ions as sulfate, nitrate, and ammonia constitute 19.0 %, EC 7.1 %, dust 3.5%, particle-bounded water (PBW) 5.3 %, and trace element oxides (TEOs), 0.9 % of PM2.5. The aerosol was acidic, with a pH of 2.5±0.4, mainly because of the abundance of organic and sulfur compounds. Diagnostic ratios and tracer concentrations indicate that most PM2.5 was emitted locally and had contributions of both pyrogenic and petrogenic sources, that biomass burning was ubiquitous during the sampling period and was the main source of PAHs, and that the relatively low PM2.5 concentrations and mutagenic potentials are consistent with low-intensity, year-long biomass burning (BB) and sugarcane pre-harvest burning in the CRV.

Urban PM2.5 concentrations in a small Colombian city and the impact associated with particle emissions generated by small-scale lime production

“…There one would expect important particle emissions not only from the principal road with 10 000 -11 000 vehicles per day that runs north-south in the valley just east of Vijes, but also from industrial and agricultural emissions taking place nearby in the valley. The Cauca River Valley is a center for sugarcane cultivation and the pre-harvest burning of sugar cane fields is an important contributor of PM concentrations in the valley (Mateus-Fontecha et al, 2022).…”

“…1), where a large fraction of the area is devoted to sugarcane cultivation and production of its derivatives. A recent analysis of the PM2.5 aerosol composition in CRV (Mateus-Fontecha et al, 2022) showed a dominant fraction of organic matter (53%), both primary and secondary, followed by salts (20%, mostly ammonium sulphate), dust (9%) and elemental carbon (7%). The authors concluded that biomass burning was a persistent source, together with traffic and fuel combustion.…”

Climate Change, Forest Fires, and Territorial Dynamics in the Amazon Rainforest: An Integrated Analysis for Mitigation Strategies

“…During wildfire events, the northern CdC experiences high temperatures, arid humidity levels, strong winds, and scant rainfall-factors that significantly promote wildfire development [9]. Notably, this region features shrubs tightly intertwined with agricultural endeavors (Figure 9), which have progressively expanded over time, augmenting the likelihood of wildfire occurrence as farmers resort to controlled burns for harvesting purposes (e.g., [12,83]), or even to shift crop types, such as illegal crops [8]. Notably, this evolving agricultural landscape has been shaped by both local dynamics and national policies enacted by the government, which have precipitated the expansion of Caqueta's agricultural frontier.…”

Biomass burning-agriculture coupling in the Orinoco savannas—Particulate matter emission scenarios

“…These aerosol flux levels are comparable to those in polluted urban (Pachón et al, 2018) or industrial areas. Finer particles, usually measured as PM2.5 (aerodynamic diameter <2.5 µm), are also emitted by operations on soils, diesel combustion for mechanization, and burning of biomass, including for land preparation and pre-harvest and crop residue management practices (Mateus-Fontecha et al, 2022). Diesel and biomass burning particles are mostly carbonaceous (soot and organic) and frequently toxic.…”