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Small-scale wood combustion is a remarkable source of organonitrates

Small-scale wood combustion is a remarkable source of organonitrates

Researchers at the University of Eastern Finland and Finnish Meteorological Institute found that batchwise combustion of spruce logs is a remarkable source of organic compounds.

Organic compounds reside both in freshly emitted particles and in particles that are formed in the atmosphere from the gaseous part of the emission through various transformation processes. A substantial fraction of the particulate emissions were organonitrates, which are an important but so far poorly characterized nitrogen-containing chemical group. A particularly high concentration of organonitrates was observed in experiments that simulated nighttime conditions. Furthermore, the ignition speed of the spruce logs was found to affect the composition and concentration of the emissions.

Organonitrates are an important chemical group regarding the atmospheric chemistry, because they possess a great potential to form secondary organic aerosols in the atmosphere. Organonitrates are mainly formed during the nighttime in oxidation reactions by ozone and nitrate radical. They are also formed during the daytime in photochemical reactions of organics in the presence of oxides of nitrogen, but they are partly readily decomposed under the influence of ultraviolet radiation. In this study, the small-scale wood combustion itself was found to be a remarkable source of organonitrates, too.

The ignition speed of wood logs plays a role

In different experiments the spruce logs were ignited by using kindlings of two different sizes. When bigger kindlings were used, the wood started to burn at a slower rate. The slower ignition increased remarkably the emissions of organic compounds and subsequently the concentrations of compounds formed through the atmospheric transformation processes. Therefore, it was concluded that burning conditions may have a substantial effect on the composition and concentration of both the freshly emitted and transformed emission.

The atmosphere never sleeps

Different kinds of transformation processes in the atmosphere are constantly going on. In these transformation processes, e.g., ozone, hydroxyl radical, and nitrate radical oxidize rapidly the organic compounds in emissions. Ozone and hydroxyl radical are key oxidizers during the daytime whereas ozone and nitrate radical during the nighttime. In this study the nighttime formation of organonitrates and transformation of the original organics in the emission were found surprisingly extensive. Furthermore, the transformation rates were relatively fast, in the order of hours.

Further information:

Senior Scientist Ari Leskinen, Finnish Meteorological Institute, phone +358 50 522 9148, ari.leskinen@fmi.fi

Researcher Petri Tiitta, Universit of Eastern Finland, phone +358 40 185 1919, petri.tiitta@uef.fi

Reference to the original article:

Tiitta P., Leskinen A., Hao L., Yli-Pirilä P., Kortelainen M., Grigonyte J., Tissari J., Lamberg H., Hartikainen A., Kuuspalo K., Kortelainen A., Virtanen A., Lehtinen K.E.J., Komppula M., Pieber S., Prévôt A.S.H., Onasch T.B., Worsnop D.R., Czech H., Zimmermann R., Jokiniemi J. & Sippula O. 2016. Transformation of logwood combustion emissions in a smog chamber: formation of secondary organic aerosol and changes in the primary organic aerosol upon daytime and nighttime aging. Atmos. Chem. Phys., 16, 13251-13269, doi:10.5194/acp-16-13251-2016

Link to the original article: http://www.atmos-chem-phys.net/16/13251/2016/


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