Quantifying primary and secondary humic-like substances in urban aerosol based on emission source characterization and a source-oriented air quality model

Abstract

<p><strong>Abstract.</strong> Humic-like substances (HULIS) are a mixture of high molecular weight, water-soluble organic compounds that are widely distributed in atmospheric aerosol. Their sources are rarely studied quantitatively. Biomass burning is generally accepted as a major primary source of ambient humic-like substances (HULIS) with additional secondary material formed in the atmosphere. However, the present study provides direct evidence that residential coal burning is also a significant source of ambient HULIS, especially in the heating season in northern China based on source measurements, ambient sampling and analysis, and apportionment with source-oriented CMAQ modeling. Emissions tests show that residential coal combustion produces 5 to 24 % of the emitted organic carbon (OC) as HULIS carbon (HULISc). Estimation of primary emissions of HULIS in Beijing indicated that residential biofuel and coal burning contribute about 70 % and 25 % of annual primary HULIS, respectively. Vehicle exhaust, industry, and power plants contributions are negligible. Average concentration of ambient HULIS was 7.5 μg/m<sup>3</sup> in atmospheric PM<sub>2.5</sub> in urban Beijing and HULIS exhibited obvious seasonal variations with the highest concentrations in winter. HULISc account for 7.2 % of PM<sub>2.5</sub> mass, 24.5 % of OC, and 59.5 % of water-soluble organic carbon, respectively. HULIS are found to correlate well with K<sup>+</sup>, Cl<sup>−</sup>, sulfate, and secondary organic aerosol suggesting its sources include biomass burning, coal combustion and secondary aerosol formation. Source apportionment based on CMAQ modeling shows residential biofuel and coal burning, secondary formation are important annual sources of ambient HULIS, contributing 57.5 %, 12.3 %, and 25.8 %, respectively.</p>

Estimating mean molecular weight, carbon number, and OM/OC with mid-infrared spectroscopy in organic particulate matter samples from a monitoring network

“…high-MW HULIS (Li et al, 2019). We also observe a decrease in mean molecular weight peak density in urban samples from winter to summer that is believed to be attributed to fragmentation during more intense photooxidation in summer Hand et al (2019); Jimenez et al (2009), for emission sources that do not change drastically between the two seasons.…”

Global review of recent source apportionments for airborne particulate matter

“… Emami and Hopke (2017) have shown that adding gases to a typical PMF data set provides additional source resolution and reduces rotational ambiguity. Li et al (2019b) provided a better resolution of PM 2.5 in Beijing by adding gases, OC/EC IMPROVE thermal fractions, and water-soluble OC and HULIS. Thus, including additional species in the data set can add to the quality of the source apportionment.…”

Significant seasonal changes in optical properties of brown carbon in the midlatitude atmosphere

“…ous studies have identified that HULIS has both direct emission sources from biomass burning, marine aerosols, and soil resuspension and indirect contribution from secondary formation (Graber and Rudich, 2006;Hoffer et al, 2006;Lin et al, 2010;Yan and Kim, 2017). Recently, residential coal combustion was suggested as an important source of HULIS during cold seasons (Tan et al, 2016;Voliotis et al, 2017;Li et al, 2019). Besides HULIS, biological aerosols (e.g., bacteria, algae, pollen, spores, fungi, plant debris, and animal tissue) are another important sources of BrC (Després et al, 2012;Pöhlker et al, 2012).…”