Pronounced increases in nitrogen emissions and deposition due to the historic 2020 wildfires in the western U.S

Anatomy of Summertime Upslope Events in Northeastern Colorado: Ammonia (NH3) Transport to the Rocky Mountains

The Transport and Transformation of Ammonia (TRANS2Am) airborne field campaign occurred over northeastern Colorado during the summers of 2021 and 2022. A subset of the TRANS2Am flights investigated easterly wind conditions capable of moving agricultural emissions of ammonia (NH3) through urban areas and into the Rocky Mountains. TRANS2Am captured 6 of these events, unveiling important commonalities. (1) NH3 enhancements are present over the mountains on summer afternoons when easterly winds are present in the foothills region. (2) The abundance of gas-phase NH3 is 1 and 2 orders of magnitude higher than particle-phase NH4+ over the mountains and major agricultural sources, respectively. (3) During thermally driven circulation periods, emissions from animal husbandry sources closer to the mountains likely contribute more to the NH3 observed over the mountains than sources located further east. (4) Transport of plumes from major animal husbandry sources in northeastern Colorado westward across the foothills requires ∼5 h. (5) Winds drive variability in the transport of NH3 into nearby mountain ecosystems, producing both direct plume transport and recirculation. A similar campaign in other seasons, including spring and autumn, when synoptic scale events can produce sustained upslope transport, would place these results in context.

Fine particle pollution during megafires contains potentially toxic elements

Wildfires that raged across Australia during the 2019-2020 'Black Summer' produced an enormous quantity of particulate matter (PM) pollution, with plumes that cloaked many urban centres and ecosystems along the eastern seaboard. This has motivated a need to understand the magnitude and nature of PM exposure, so that its impact on both built and natural environments can be more accurately assessed. Here we present the potentially toxic fingerprint of PM captured by building heating, ventilation, and air conditioning filters in Sydney, Australia during the peak of the Wildfires, and from ambient urban emissions one year later (Reference period). Atmospheric PM and meteorological monitoring data were also assessed to determine the magnitude and source of high PM exposure. The wildfires were a major source of PM pollution in Sydney, exceeding the national standards on 19 % of days between November-February. Wildfire particles were finer and more spherical compared to Reference PM, with count median diameters of 892.1 ± 23.1 versus 1484.8 ± 96.7 nm (mean ± standard error). On an equal-mass basis, differences in potentially toxic elements were predominantly due to higher SO42--S (median 20.4 vs 4.7 mg g-1) and NO3--N (2.4 vs 1.2 mg g-1) in Wildfire PM, and higher PO43--P (10.4 vs 1.4 mg g-1) in Reference PM. Concentrations of remaining elements were similar or lower than Reference PM, except for enrichments to F-, Cl-, dissolved Mn, and particulate Mn, Co and Sb. Fractional solubilities of trace elements were similar or lower than Reference PM, except for enhanced Hg (12.1 vs 1.0 %) and greater variability in Cd, Hg and Mn solubility, which displayed upper quartiles exceeding that of Reference PM. These findings contribute to our understanding of human and ecosystem exposures to the toxic components of mixed smoke plumes, especially in regions downwind of the source.

Wildfires in the western United States are mobilizing PM2.5-associated nutrients and may be contributing to downwind cyanobacteria blooms

Wildfire activity is increasing in the continental U.S. and can be linked to climate change effects, including rising temperatures and more frequent drought conditions. Wildfire emissions and large fire frequency have increased in the western U.S., impacting human health and ecosystems. We linked 15 years (2006-2020) of particulate matter (PM2.5) chemical speciation data with smoke plume analysis to identify PM2.5-associated nutrients elevated in air samples on smoke-impacted days. Most macro- and micro-nutrients analyzed (phosphorus, calcium, potassium, sodium, silicon, aluminum, iron, manganese, and magnesium) were significantly elevated on smoke days across all years analyzed. The largest percent increase was observed for phosphorus. With the exception of ammonium, all other nutrients (nitrate, copper, and zinc), although not statistically significant, had higher median values across all years on smoke vs. non-smoke days. Not surprisingly, there was high variation between smoke impacted days, with some nutrients episodically elevated >10 000% during select fire events. Beyond nutrients, we also explored instances where algal blooms occurred in multiple lakes downwind from high-nutrient fires. In these cases, remotely sensed cyanobacteria indices in downwind lakes increased two to seven days following the occurrence of wildfire smoke above the lake. This suggests that elevated nutrients in wildfire smoke may contribute to downwind algal blooms. Since cyanobacteria blooms can be associated with the production of cyanotoxins and wildfire activity is increasing due to climate change, this finding has implications for drinking water reservoirs in the western United States, and for lake ecology, particularly alpine lakes with otherwise limited nutrient inputs.

Trace gas emissions from laboratory combustion of leaves typically consumed in forest fires in Southwest China

Forest fires are becoming increasingly severe and frequent due to global climate change. Trace gases emitted from forest fires significantly affect atmospheric chemistry and climate change on a regional and global scale. Forest fires occur frequently in Southwest China, but systematic studies on trace gas emissions from forest fires in Southwest China are rare. Leaves of seven typical vegetation fuels based on their prominence in forest fires consumption in Southwest China were burned in a self-designed combustion device and the emission factors of eighteen trace gases (greenhouse gases, non-methane organic gases, nitrogenous gases, hydrogen chloride, and sulfur dioxide) at specific combustion stages (flaming and smoldering) were determined by using Fourier transform infrared spectroscopy, respectively. The emission factors data presented were compared with previous studies and can aid in the construction of an emission inventory. Pine needle combustion released a greater amount of methane in the smoldering stage than other broadleaf combustion. Peak values of emission factors for methane and non-methane organic gas are emitted by the smoldering of vegetation (Pinus kesiya and Pinus yunnanensis), which is endemic to forest fires in Southwest China. The emission factor for oxygenated volatile organic compounds (OVOCs) in the smoldering stage is greater than the flaming stage. This work established the relationship between modified combustion efficiency (MCE) with emission factors of hydrocarbons (except acetylene) and OVOCs. The results show that exponential fitting is more suitable than linear fitting for the seven leaf fuels (four broadleaf and three coniferous). However, the emission factors from the combustion of three coniferous fuels relative to all fuels are linear with MCE. Findings demonstrated that different combustion stages and fuel types have significant impacts on the emission factors, which also highlighted the importance of studying regional emissions.