Chemical properties, sources and size-resolved hygroscopicity of submicron black-carbon-containing aerosols in urban Shanghai

Abstract

Abstract. Refractory black carbon (rBC) aerosols play an important role in air quality and climate change, yet highly time-resolved and detailed investigations on the physicochemical properties of rBC and its associated coating are still scarce. In this work, we used a laser-only Aerodyne soot particle aerosol mass spectrometer (SP-AMS) to exclusively measure rBC-containing (rBCc) particles, and we compared their properties with those of the total nonrefractory submicron particles (NR-PM1) measured in parallel by a high-resolution AMS (HR-AMS) in Shanghai. Observations showed that, overall, rBC was thickly coated, with an average mass ratio of coating to rBC core (RBC) of ∼5.0 (±1.7). However, the ratio of the mass of the rBC-coating species to the mass of those species in NR-PM1 was only 19.1 (±4.9) %; sulfate tended to condense preferentially on non-rBC particles, so the ratio of the sulfate on rBC to the NR-PM1 sulfate was only 7.4 (±2.2) %, while the majority (72.7±21.0 %) of the primary organic aerosols (POA) were associated with rBC. Positive matrix factorization revealed that organics emitted from cooking did not coat rBC, and a portion of the organics that coated rBC was from biomass burning; such organics were unidentifiable in NR-PM1. Small rBCc particles were predominantly from traffic, while large-sized ones were often mixed with secondary components and typically had a thick coating. Sulfate and secondary organic aerosol (SOA) species were generated mainly through daytime photochemical oxidation (SOA formation, likely associated with in situ chemical conversion of traffic-related POA to SOA), while nocturnal heterogeneous formation was dominant for nitrate; we also estimated an average time of 5–19 h for those secondary species to coat rBC. During a short period that was affected by ship emissions, particles were characterized as having a high vanadium concentration (on average 6.3±3.1 ng m−3) and a mean vanadium/nickel mass ratio of 2.0 (±0.6). Furthermore, the size-resolved hygroscopicity parameter (κrBCc) of rBCc particles was obtained based on their full chemical characterization, and was parameterized as κrBCc(x)=0.29–0.14 × exp⁡(-0.006×x) (where x ranges from 150 to 1000 nm). Under critical supersaturations (SSC) of 0.1 % and 0.2 %, the D50 values were 166 (±16) and 110 (±5) nm, respectively, and 16 (±3) % and 59 (±4) %, respectively, of the rBCc particles by number could be activated into cloud condensation nuclei (CCN). Our findings are valuable for advancing the understanding of BC chemistry as well as the effective control of atmospheric BC pollution.

Impacts of elevated anthropogenic emissions on physicochemical characteristics of BC-containing particles over the Tibetan Plateau

“…5b) at both sites, which was consistent with the observation in central TP (Wang et al, 2017). OA took up a higher proportion in BC coating in Lulang compared to Xihai, Shanghai (Cui et al, 2022) and Fresno (Collier et al, 2018).…”

“…In some previous study, elemental carbon (EC) approximately equivalent to BC was measured. BC concentrations of TP demonstrated comparable levels across various campaigns, amounting to approximately 25% or less of the BC concentration observed in metropolitan areas (Cui et al, 2022). The BC concentration in Xihai was consistent with that of a nearby site in the northeast TP (Table 1).…”

Improving BC Mixing State and CCN Activity Representation With Machine Learning in the Community Atmosphere Model Version 6 (CAM6)

“…In contrast, the median values of R BC are ∼10/20 for MAM4-ML/MAM4-default in source regions dominated by anthropogenic fossil fuel emission, such as Europe (median R BC = 13/25), India (median R BC = 10/19), and Eastern China (median R BC = 7/15). Previous observational studies have also measured higher R BC values (>10, Cappa et al (2012), Massoli et al (2015a), McMeeking et al (2014) in North America than those observed at polluted urban cities of China (<5, Cao et al (2022), Cui et al (2022), Wang et al (2019b), Wu et al (2019)). Furthermore, laboratory experiments by showed that R BC from biomass burning was larger than that from solid fuel and traffic sources, and they also simulated the higher R BC over the United States, Amazon, and Western and Middle Africa by the 3D Global Model of Aerosol Processes model (GLOMAP).…”

Characteristics of fine particle matter at the top of Shanghai Tower

“…In summer, the fraction at a rural site (Zhao et al, 2020) was found to be lower but close to this study. According to Cui et al (2022), the proportion of NO 3 was as high as 26.0 % in the late fall of 2018. For a similar period (November) in 2019, the ratio at SHT was 27.2 %.…”