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.

The Colombian Orinoco savannas (254 thousand km2), also known as Orinoquia or Llanos, have been steadily transformed into pastures for more than a century, and since the 1990s, into commodity crop intensified production. The cropland area expanded at 12% yr−1 during the 2007–2018 period (65% larger than in 1996–2007). Yet, we estimate that cattle ranching occupied ten times more area (34%) than cropland (3.2%) in 2018. The rest of Orinoquia, including indigenous reservations and protected areas, was in a semi-natural state, although also exposed to seasonal fire. The three main crops, oil palm, corn, and rice (72% of the sown area in 2017), accounted for 68% of the expansion, with permanent crops expanding two times faster (18% yr−1) than short-cycle crops. An extrapolation of trends indicates that the cultivated area will double by 2040 (reaching 20 thousand km2), with oil palm as the dominant crop. Satellite measurements show that 7% of Orinoquia burned every year during the 1997–2016 period, yet with large spatial and interannual variations (±26%), and significant decrease trends (up to −4% yr−1). Up to 40% of the burned area (BA) interannual variability was linked to irregular rainfall and drought. The areas with the larger fractional BA were also those with the least fractional cropland cover. A model developed to describe this coupling, along with rainfall and other effects, successfully explained most of Orinoquia’s BA variability (r2 = 0.93). The fitted model indicates that each sown hectare reduced the BA by 0.17 ha. This model predicts that the combination of cropland expansion and independent BA decline will lead to a fourfold reduction of Orinoquia’s BA by 2040 referred to 1997. Orinoquia’s crop production generated 3 Gg of PM10 (particulate matter <10 µm) in 2016, mostly from short-cycle crops, while biomass burning generated 57 Gg, i.e., 95% of the combined emissions. These are expected to halve during the 2017–2040 period, despite an 83% increase in crop production emissions, as total and seasonal emissions will remain controlled by biomass burning. Such a large pollution burden reduction should have tremendous positive impacts on public health in Orinoquia and the Andes.

Abstract. Agro-industrial areas are frequently affected by various sources of atmospheric pollutants that negatively impact public health and ecosystems. However, air quality in these areas is infrequently monitored because of their lower population density compared to large cities, especially in developing countries. The Cauca River Valley (CRV) is an agro-industrial region in Southwest Colombia, where a large fraction of the area is devoted to sugarcane and derivatives production. 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. For this, a sampling campaign was carried out at a representative site of 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. Mean PM2.5 was 14.38 ± 4.35 ug m−3, and the most abundant constituent was organic material (52.99 % ± 17.79 %), followed by ammonium sulfate (16.12 % ± 3.98 %), and elemental carbon (6.95 % ± 2.52 %), which indicates 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. The diagnostic ratios applied to organic compounds revealed the influence of petrogenic and pyrogenic sources. Principal component analysis identified the influence of traffic-generated road dust, secondary aerosol formation, gasoline and diesel combustion vehicle exhaust, vegetative detritus, and resuspended agriculture soil. However, no single component was dominant nor explained the CRV PM2.5 chemical species variance. Many components had equally important roles instead. Likewise, sugarcane pre-harvest burning, a frequent activity in CRV, was not identified as an independent component. This aerosol and trace gas source contributed to various components and was correlated to the formation of secondary aerosols.

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The Colombian Orinoco savannas (254 thousand km2), also known as Orinoquia or Llanos, have been steadily transformed into pastures for more than a century, and since the 1990s, into commodity crop intensified production. The cropland area expanded at 12% yr-1 during the 2007-2018 period (65% larger than in 1996-2007). Yet, we estimate that cattle ranching occupied ten times more area (34%) than cropland (3.2%) in 2018. The rest of Orinoquia, including indigenous reservations and protected areas, was in a semi-natural state, although also exposed to seasonal fire. The three main crops, oil palm, corn, and rice (72% of the sown area in 2017), accounted for 68% of the expansion, with permanent crops expanding two times faster (18% yr-1) than short-cycle crops. An extrapolation of trends indicates that the cultivated area will double by 2040 (reaching 20 thousand km2), with oil palm as the dominant crop. Satellite measurements show that 7% of Orinoquia burned every year during the 1997-2016 period, yet with large spatial and interannual variations (±26%), and significant decrease trends (up to -4% yr-1). Up to 40% of the burned area (BA) interannual variability was linked to irregular rainfall and drought. The areas with the larger fractional BA were also those with the least fractional cropland cover. A model developed to describe this coupling, along with rainfall and other effects, successfully explained most of Orinoquia’s BA variability (r2 = 0.93). The fitted model indicates that each sown hectare reduced the BA by 0.17 ha. This model predicts that the combination of cropland expansion and independent BA decline will lead to a fourfold reduction of Orinoquia’s BA by 2040 referred to 1997. Orinoquia’s crop production generated 3 Gg of PM10 (particulate matter < 10 µm) in 2016, mostly from short-cycle crops, while biomass burning generated 57 Gg, i.e., 95% of the combined emissions. These are expected to halve during the 2017-2040 period, despite an 83% increase in crop production emissions, as total and seasonal emissions will remain controlled by biomass burning. Such a large pollution burden reduction should have tremendous positive impacts on public health in Orinoquia and the Andes.