Index Geophysics

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

Organic aerosols (OA) derived from small-scale wood combustion emissions are not well represented by current emissions inventories and models, although they contribute substantially to the atmospheric particulate matter (PM) levels. In this work, a 29 m³ smog chamber in the ILMARI facility of the University of Eastern Finland was utilized to investigate the formation of secondary organic aerosol (SOA) from a small-scale modern masonry heater commonly used in northern Europe. Emissions were oxidatively aged in the smog chamber for a variety of dark (i.e., O₃ and NO₃) and UV (i.e., OH) conditions, with OH concentration levels of (0.5–5)  ×  10⁶ molecules cm⁻³, achieving equivalent atmospheric aging of up to 18 h. An aerosol mass spectrometer characterized the direct OA emissions and the SOA formed from the combustion of three wood species (birch, beech and spruce) using two ignition processes (fast ignition with a VOC-to-NO_<i>x</i> ratio of 3 and slow ignition with a ratio of 5).<br><br>Dark and UV aging increased the SOA mass fraction with average SOA productions 2.0 times the initial OA mass loadings. SOA enhancement was found to be higher for the slow ignition compared with fast ignition conditions. Positive matrix factorization (PMF) was used to separate SOA, primary organic aerosol (POA) and their subgroups from the total OA mass spectra. PMF analysis identified two POA and three SOA factors that correlated with the three major oxidizers: ozone, the nitrate radical and the OH radical. Organonitrates (ONs) were observed to be emitted directly from the wood combustion and additionally formed during oxidation via NO₃ radicals (dark aging), suggesting small-scale wood combustion may be a significant ON source. POA was oxidized after the ozone addition, forming aged POA, and after 7 h of aging more than 75 % of the original POA was transformed. This process may involve evaporation and homogeneous gas-phase oxidation as well as heterogeneous oxidation of particulate organic matter. The results generally prove that logwood burning emissions are the subject of intensive chemical processing in the atmosphere, and the timescale for these transformations is relatively short, i.e., hours.

Tiitta, Petri

Leskinen, Ari

Hao, Liqing

Yli-Pirilä, Pasi

Kortelainen, Miika

Grigonyte, Julija

Tissari, Jarkko

Lamberg, Heikki

Hartikainen, Anni

Kuuspalo, Kari

Kortelainen, Aki-Matti

Virtanen, Annele

Lehtinen, Kari E. J.

Komppula, Mika

Pieber, Simone

Prévôt, André S. H.

Onasch, Timothy B.

Worsnop, Douglas R.

Czech, Hendryk

Zimmermann, Ralf

Jokiniemi, Jorma

Sippula, Olli

2018-09-15

Text

application/pdf

10.5194/acp-16-13251-2016

https://acp.copernicus.org/articles/16/13251/2016/

eISSN: 1680-7324

eng