ReviewMeasurement of humic-like substances in aerosols: A review

- Diverse operational definitions of HULIS were found to focus on several specific versions of definitions.
- The global map of presence and abundance of HULIS was shown.
- Size distribution and spatial-temporal variation of HULIS were summarized.
- Dominant HULIS sources were recognized as biomass burning and secondary reactions.
- Detailed formation pathways of HULIS were categorized.

Aerosol-phase humic-like substances (HULIS) have received increasingly attention due to their universal ambient presence, active participation in atmospheric chemistry and important environmental and health effects. In last decade, intensive field works have promoted development of quantification and analysis method, unearthed spatio-temporal variation, and proved evidence for source identification of HULIS. These important developments were summarized in this review to provide a global perspective of HULIS. The diverse operational HULIS definitions were gradually focused onto several versions. Although found globally in Europe, Asia, Australasia and North America, HULIS are far more typical in continental and near-ground aerosols. HULIS concentrations varied from <1 μg/m3 to >13 μg/m3, with their carbon fraction making up 9%-72% of water soluble organic carbon. Dominant HULIS source was suggested as secondary processes and biomass burning, with the detailed formation pathways suggested and verified in laboratory works.