Measurement report: Source apportionment of carbonaceous aerosol using dual-carbon isotopes (¹³C and ¹⁴C) and levoglucosan in three northern Chinese cities during 2018–2019

In this study, we investigated the characteristics of and changes in the sources of carbonaceous aerosols in northern Chinese cities after the implementation of the Action Plan for Air Pollution Prevention and Control in 2013. We collected PM2.5 samples from three representative inland cities, viz. Beijing (BJ), Xi’an (XA), and Linfen (LF) from January 2018 to April 2019. Elemental carbon (EC), organic carbon (OC), levoglucosan, stable carbon, and radiocarbon were measured in PM2.5 to quantify the sources of carbonaceous aerosol employing Latin hypercube sampling. The best estimate of source apportionment showed that the emissions from liquid fossil fuels contributed 33.6 ± 12.9 %, 26.6 ± 16.4 %, and 24.6 ± 13.4 % of the total carbon (TC) in BJ, XA, and LF, whereas coal combustion contributed 11.2 ± 9.1 %, 19.2 ± 12.3 %, and 39.2 ± 20.5 %, respectively. Non-fossil sources accounted for 55 ± 11 %, 54 ± 10 %, and 36 ± 14 % of the TC in BJ, XA, and LF, respectively. In XA, 48.34 ± 32.01 % of non-fossil sources was attributed to biomass burning. The highest contributors to OC in LF and XA were fossil sources (65.4 ± 14.9 % and 44.9 ± 9.5 %, respectively), whereas that in BJ was non-fossil sources in BJ (56.1 ± 16.7 %). The main contributors to EC were fossil sources, accounting for 92.9 ± 6.13 %, 69.9 ± 20.9 %, and 90.8 ± 9.9 % of the total EC in BJ, XA, and LF, respectively. The decline (6–17 %) in fossil source contributions in BJ and XA since the implementation of the Action Plan indicates the effectiveness of air quality management. We suggest that measures targeted to each city should be strengthened in the future.

Cellulose in atmospheric particulate matter

The spatiotemporal variations of free cellulose concentrations in atmospheric particles, as a proxy for plant debris, were investigated using a novel HPLC-PAD method. Filter samples were taken from nine sites of varying characteristics across France and Switzerland, with sampling covering all seasons. Concentrations of cellulose, as well as carbonaceous aerosol and other source-specific chemical tracers (e.g. Elemental Carbon (EC), levoglucosan, polyols, trace metals, and glucose) were quantified. Annual mean free cellulose concentrations within PM10 ranged from 29 ± 38 ng m−3 at Bern (urban site) to 284 ± 225 ng m−3 at Payerne (rural site). Concentrations were considerably higher during episodes, with spikes exceeding 1150 and 2200 ng m−3 at Payerne and ANDRA-OPE (rural site), respectively. A clear seasonality, with highest cellulose concentrations during summer and autumn, was observed at all rural and some urban sites. However, some urban locations exhibited a weakened seasonality. Contributions of cellulose-carbon to total organic carbon are moderate on average (0.7–5.9 %), but much greater during ‘episodes’, reaching close to 20 % at Payerne. Cellulose concentrations correlated poorly between sites, even a ranges of about 10 km, indicating the localised nature of the sources of atmospheric plant debris. With regards to these sources, correlations between cellulose and typical biogenic chemical tracers (polyols and glucose) were moderate to strong (Rs 0.28−0.78, p < 0.0001) across the nine sites. Seasonality was strongest at sites with stronger biogenic correlations, suggesting the main source of cellulose arises from biogenic origins. A second input to ambient plant debris concentrations was suggested via resuspension of plant matter at several urban sites, due to moderate cellulose correlations with mineral dust tracers, Ca2+ and Ti metal (Rs 0.28−0.45, p < 0.007). No correlation was obtained with the biomass burning tracer (levoglucosan), an indication that this is not a source of atmospheric cellulose. Finally, an investigation into the interannual variability of atmospheric cellulose across the Grenoble metropole area was completed. It was shown that concentrations and sources of ambient cellulose can vary considerably between years. All together, these results deeply improve our knowledge on the phenomenology of plant debris within ambient air.

The outflow of Asian biomass burning carbonaceous aerosol into the upper troposphere and lower stratosphere in spring: radiative effects seen in a global model

Biomass burning (BB) over Asia is a strong source of carbonaceous aerosols during spring. From ECHAM6–HAMMOZ model simulations and satellite observations, we show that there is an outflow of Asian BB carbonaceous aerosols into the upper troposphere and lower stratosphere (UTLS) (black carbon: 0.1 to 6 ng m−3 and organic carbon: 0.2 to 10 ng m−3) during the spring season. The model simulations show that the greatest transport of BB carbonaceous aerosols into the UTLS occurs from the Indochina and East Asia region by deep convection over the Malay Peninsula and Indonesia. The increase in BB carbonaceous aerosols enhances atmospheric heating by 0.001 to 0.02 K d−1 in the UTLS. The aerosol-induced heating and circulation changes increase the water vapor mixing ratios in the upper troposphere (by 20–80 ppmv) and in the lowermost stratosphere (by 0.02–0.3 ppmv) over the tropics. Once in the lower stratosphere, water vapor is further transported to the South Pole by the lowermost branch of the Brewer–Dobson circulation. These aerosols enhance the in-atmosphere radiative forcing (0.68±0.25 to 5.30±0.37 W m−2), exacerbating atmospheric warming, but produce a cooling effect on climate (top of the atmosphere – TOA: -2.38±0.12 to -7.08±0.72 W m−2). The model simulations also show that Asian carbonaceous aerosols are transported to the Arctic in the troposphere. The maximum enhancement in aerosol extinction is seen at 400 hPa (by 0.0093 km−1) and associated heating rates at 300 hPa (by 0.032 K d−1) in the Arctic.