Fireworks Send Barium Soaring 1000-Fold as Particles Transform Within Hours Over Guangzhou

When fireworks lit up the sky over Guangzhou, China, during the 2024 Spring Festival, they did more than paint the night in green and gold. They flooded the air with barium, a metal used to produce vivid green flames, at concentrations reaching as much as 1000 times above background levels in hourly peaks. A month-long monitoring campaign across four sites in the city has now traced what happens to those metal-rich particles after they disperse, revealing that they undergo rapid chemical transformation within hours of being launched.

The study, published in Atmospheric Chemistry and Physics, combined continuous online measurements of barium mass concentrations with single-particle aerosol mass spectrometry, known as SPAMS, at four monitoring stations spanning Guangzhou from 1 to 29 February 2024. The period covered the two main legal firework windows of the Chinese calendar: the Spring Festival on 9 and 10 February and the Lantern Festival on 24 February. Researchers from Jinan University, the Guangzhou Institute of Geochemistry, and partner institutions tracked both the bulk amount of barium in fine particles and the individual chemical fingerprints of tens of thousands of single particles.

The scale of the firework signal was striking. During the Spring Festival episode, barium mass concentrations rose by 17 to 40 times compared with the preceding background period, while potassium climbed 9 to 23 times, chloride 2 to 3 times, and heavy metals such as copper and lead also increased. Hourly peaks of barium and barium-containing particle counts exceeded background levels by roughly two orders of magnitude on average, with individual hours reaching up to 1000-fold enhancements. In the 0.5 to 1.0 micrometre size range, the number of barium-containing particles surged from 2193 during background conditions to 24,624 during firework periods, an 11.2-fold increase that the authors note exceeds the 6.7-fold rise reported during Milan fireworks displays.

Perhaps the most politically intriguing finding concerns where the pollution peaked. The highest concentrations were recorded not in the urban core, where fireworks are completely banned, but at Panyu University City, a suburban site in a restricted zone where fireworks are permitted only in designated towns during festival periods. There, peak barium reached 3411 nanograms per cubic metre and fine particulate matter peaked at 89 micrograms per cubic metre. The urban-core site at Gongyuanqian, despite having a far higher population density of 28,400 people per square kilometre compared with 5327 at Panyu, recorded lower peaks. The researchers are careful about this contrast: they describe it as consistent with a potential mitigating influence of stricter controls, while acknowledging that local firework activity, enforcement intensity, meteorology, atmospheric transport, and proximity to sources may all have contributed, and that the interpretation warrants verification with enforcement records and wind field analysis.

The single-particle data revealed the aging story in remarkable detail. Two particle categories stood out. One type, labelled OClN, was rich in oxygen, chloride, and nitrate, carrying strong signals for barium, barium oxide, chloride, and nitrate in its mass spectrum. The other, labelled N, was dominated by nitrate, with nitrate and nitrite accounting for about 70 percent of the total negative ion signal. The team interpreted OClN particles as a relatively early stage of atmospheric aging and N particles as a more advanced stage, a classification grounded in the observed chemical evolution rather than in direct sampling of fresh emissions near firework sources, a limitation the authors state explicitly.

Several independent lines of evidence supported this progression. During the transition from firework hours to post-firework daytime hours, the number fraction of chloride-containing particles fell from 24 to 21 percent, the relative chloride signal declined from 0.059 to 0.040, and the nitrate signal rose from 0.355 to 0.415. Time series analysis showed an inverse relationship between OClN and N particle counts during intense emission periods, with a correlation coefficient of minus 0.709. Most tellingly, there was a lag of roughly 9 to 10 hours between the peaks of OClN and N particles, and a lag of 2 to 4 hours between gaseous nitrogen dioxide and particulate nitrate, patterns the authors say point to secondary nitrate formation as an important aging pathway.

The aging was not purely chemical. Barium-containing particles also physically mixed with aluminium- and magnesium-containing particles, which preferentially associated with the early-aged OClN type in 60 to 80 percent of cases, compared with only 20 to 40 percent for the more processed N particles. The researchers interpret this as direct observation of coagulation during early aging, a pathway that complements the chemical conversion of chloride to nitrate. Spatial patterns reinforced the temporal ones: the suburban Nansha site showed the highest ratios of early-aged to aged particles, consistent with its proximity to active emission zones, while the background site showed predominantly fully processed, nitrate-saturated particles shaped by regional transport.

An important caveat runs through the chemical interpretation. Fireworks contain nitrate-based oxidizers such as potassium nitrate and barium nitrate, which can emit primary nitrate-containing particles directly upon combustion. The authors therefore cannot attribute the observed nitrate enrichment solely to secondary atmospheric processing, and they state that their dataset cannot fully quantify the relative contributions of primary emissions and secondary formation. They also note that the nighttime coexistence of ozone and nitrogen dioxide is consistent with the well-known N2O5 hydrolysis pathway for nitrate formation, while moderate humidity of about 60 percent during peak events suggests additional routes, such as heterogeneous uptake of nitric acid on chlorine-rich particles, may also have operated. Distinguishing among these mechanisms, they write, will require laboratory studies and thermodynamic modeling.

The team also offered a preliminary screening-level health assessment. Using an oral reference dose for barium as a surrogate because no inhalation reference concentration is available, they calculated hazard quotients ranging from about 6.11 times 10 to the minus 8 to 2.77 times 10 to the minus 5 for children and from 3.44 times 10 to the minus 8 to 1.56 times 10 to the minus 5 for adults across all sites, all far below the threshold of concern of 1. Hazard quotients during the firework episode were one to two orders of magnitude higher than during background periods, and children showed higher values than adults because of their greater respiratory rate per unit body weight. The authors stress that these estimates rely on period-specific averages, that the oral surrogate may not capture inhalation-specific bioavailability, and that the health risk of barium particles depends on their chemical form, which was not directly measured. Because barium concentrations spiked sharply for only a few hours, and no formal acute hazard quotient could be calculated without an established acute reference value, they call for further evaluation of short-duration peak exposures using inhalation-specific toxicity benchmarks, particularly for children and people with respiratory or cardiovascular conditions.

Beyond the specific chemistry of barium, the study demonstrates what single-particle analysis can reveal about the fate of metal aerosols in urban air. The observed shift toward smaller particle sizes during chloride-to-nitrate conversion may enhance the potential for respiratory deposition, and the preferential association of aluminium and magnesium with early-aged particles suggests coagulation is most active in the first hours after emission, potentially altering particle hygroscopicity and reactivity. The authors propose their approach as a framework for investigating aging mechanisms of other firework-emitted metals, and they recommend that future work combine near-source sampling with high-time-resolution tracer measurements to separate primary from secondary nitrate, while characterizing how barium speciation, solubility, and bioavailability change as particles age. For cities weighing firework restrictions, the findings add a new dimension: the particles fireworks release do not simply dilute away, but continue to evolve chemically for hours, potentially influencing local air quality before any regional transport occurs.

Subject of Research: Atmospheric aging and transformation of firework-derived barium-containing aerosol particles in Guangzhou, China

Article Title: Evolution of firework-related barium aerosols: insights from single-particle analysis and mass concentration monitoring

Article References: Lian, X., Pei, C., Sun, W., Lv, C., Huang, K., Lei, L., Huang, B., Cheng, C., Zhang, G., Bi, X., Zhou, Z., & Li, M. (2026). Evolution of firework-related barium aerosols: insights from single-particle analysis and mass concentration monitoring. Atmospheric Chemistry and Physics, 26(20), 15101-15115. https://doi.org/10.5194/acp-26-15101-2026

Image Credits: AI Generated

DOI: 10.5194/acp-26-15101-2026

Keywords: fireworks, barium, aerosols, air quality, single-particle analysis, SPAMS, nitrate formation, atmospheric chemistry, Guangzhou, Chinese Spring Festival, PM2.5, particulate matter