Extreme levels and chemistry of PM from the consumer fireworks in the Netherlands

Mass concentrations of Particulate Matter (PM) in New-Year's nights can be high in the Netherlands because of the unconstrained use of consumer fireworks. In the study presented here the chemical compounds of the PM were determined. It is for the first time that this information was used to deduced the average composition of the explosive mixture/black powder. Measurements were made during the turn of the year 2007–2008 at an urban background location, when hourly PM10 mass concentrations exceeded 2000 μg m−3 at street sites. These extreme levels were due to the stagnant weather conditions occurring that night. The on-line artefact-free “MARGA” was deployed for assessment of the major compounds. These were found to be the (hygroscopic) salts KCl, MgSO4 and K2SO4. The mass ratio of sulphur and potassium showed that a standard black powder mix is used as explosive. The potassium was for 65% present as KCl. This is the reduction product of the oxidiser KClO4, which is hence the main oxidiser. The rest of the potassium was present in the form of K2SO4. We proved that this compound derives from the “standard” oxidiser KNO3 of black powder. The formation of the SO42--salts is explained as follows. The sulphur in the black powder oxidises to H2SO4. This compound reacts with the reduction product of the KNO3 to K2SO4. MgSO4 forms in a reaction of the main colouring agent magnesium with the H2SO4. The full composition of the PM, including carbonaceous material and trace metals, was obtained from an analysis of 24-hr filter samples. This showed that the mentioned salts comprised about half of the mass, while almost all of the remainder is “carbon” deriving from the incomplete combustion of the cardboard wrapping. About 85% of the PM10 is in the more harmful PM2.5.