Impacts of COVID-19 on Black Carbon in Two Representative Regions in China: Insights Based on Online Measurement in Beijing and Tibet.

Under the influence of Coronavirus Disease 2019 (COVID-19), China conducted a nationwide lockdown (LD) which significantly reduced anthropogenic emissions. To analyze the different impacts of COVID-19 on black carbon (BC) in the two representative regions in China, one-year continuous online measurements of BC were conducted simultaneously in Beijing and Tibet. The average concentration in the LD period was 20% higher than that in the pre-LD period in Beijing, which could be attributed to the increase of transport from southwestern neighboring areas and enhanced aged BC. In contrast to megacity, the average concentration of BC in Tibet decreased over 70% in the LD period, suggesting high sensitivity of plateau background areas to the anthropogenic emission reduction in South Asia. Our study clearly showed that BC responded very differently in megacity and background areas to the change of anthropogenic emission under the lockdown intervention.

Application of direct thermal desorption gas chromatography time-of-flight mass spectrometry for determination of nonpolar organics in low-volume samples from ambient particulate matter and personal samplers.

Direct thermal desorption and in-situ derivatization thermal desorption methods in conjunction with gas chromatography time-of-flight mass spectrometry have been characterized and evaluated for analysis of trace components from filters loaded with ambient particulate matter (PM). The limits of quantification were in the range of 7-24 pg for n-alkanes, 20 pg for hopanes, and 4-22 pg for polycyclic aromatic hydrocarbons (PAH). The limit of quantification was defined as the minimum amount of substance that conforms to the minimum distinguishable signal plus 9 times the standard deviation of this background signal from PM-loaded filters. The method has been successfully applied to low-volume samples from ambient PM collected with stationary and personal samplers. Stationary samples were collected in winter 2008 and 2010 in Augsburg, Germany. Sample aliquots of 0.2-0.3 m³ from stationary sampling were analyzed. High diurnal variation in concentration and source contribution was found especially during periods with low wind speed and low mixing layer height. High contributions of solid fuel combustion (wood and coal) were found in evening and nighttime samples, leading to peak PAH concentrations at midnight more than 10 times higher than at noon. Finally, the method was applied to samples collected by means of a personal sampler, i.e. a micro aethalometer, in Xi'an, China. Quantitative data on n-alkanes, hopanes, and PAH were obtained from sample volumes of 17 and 24 l. The impact of different sources such as vehicular and biogenic emissions could be distinguished.

Spectral dependence of aerosol light absorption at an urban and a remote site over the Tibetan Plateau.

We present a study of aerosol light absorption by using a 7-wavelength Aethalometer model AE33 at an urban site (Lhasa) and a remote site (Lulang) in the Tibetan Plateau. Approximately 5 times greater aerosol absorption values were observed at Lhasa (53±46Mm-1 at 370nm and 20±18Mm-1 at 950nm, respectively) in comparison to Lulang (15±19Mm-1 at 370nm and 4±5Mm-1 at 950nm, respectively). Black carbon (BC) was the dominant light absorbing aerosol component at all wavelengths. The brown carbon (BrC) absorption at 370nm is 32±15% of the total aerosol absorption at Lulang, whereas it is 8±6% at Lhasa. Higher value of absorption Ångström exponent (AAE, 370-950nm) was obtained for Lulang (1.18) than that for Lhasa (1.04) due to the presence of BrC. The AAEs (370-950nm) of BrC were directly extracted at Lulang (3.8) and Lhasa (3.3). The loading compensation parameters (k) increased with wavelengths for both sites, and lower values were obtained at Lulang than those observed at Lhasa for all wavelengths. This study underlines the relatively high percentage of BrC absorption contribution in remote area compared to urban site over the Tibetan Plateau.

Comparison of continuous and filter-based carbon measurements at the Fresno supersite.

Results from six continuous and semicontinuous black carbon (BC) and elemental carbon (EC) measurement methods are compared for ambient samples collected from December 2003 through November 2004 at the Fresno Supersite in California. Instruments included a multi-angle absorption photometer (MAAP; lambda = 670 nm); a dual-wavelength (lambda = 370 and 880 nm) aethalometer; seven-color (lambda = 370, 470, 520, 590, 660, 880, and 950 nm) aethalometers; the Sunset Laboratory carbon aerosol analysis field instrument; a photoacoustic light absorption analyzer (lambda = 1047 nm); and the R&P 5400 ambient carbon particulate monitor. All of these acquired BC or EC measurements over periods of 1 min to 1 hr. Twenty-four-hour integrated filter samples were also acquired and analyzed by the Interagency Monitoring of Protected Visual Environments (IMPROVE) thermal/optical reflectance carbon analysis protocol. Site-specific mass absorption efficiencies estimated by comparing light absorption with IMPROVE EC concentrations were 5.5 m2/g for the MAAP, 10 m2/g for the aethalometer at a wavelength of 880 nm, and 2.3 m2/g for the photoacoustic analyzer; these differed from the default efficiencies of 6.5, 16.6, and 5 m2/g, respectively. Scaling absorption by inverse wavelength did not provide equivalent light absorption coefficients among the instruments for the Fresno aerosol measurements. Ratios of light absorption at 370 nm to those at 880 nm from the aethalometer were nearly twice as high in winter as in summer. This is consistent with wintertime contributions from vehicle exhaust and from residential wood combustion, which is believed to absorb more shorter-wavelength light. To reconcile BC and EC measurements obtained by different methods, a better understanding is needed of the wavelength dependence of light-absorption and mass-absorption efficiencies and how they vary with different aerosol composition.