New insights into PM<sub>2.5</sub> chemical composition and sources in two major cities in China during extreme haze events using aerosol mass spectrometry

Abstract

During winter 2013-2014 aerosol mass spectrometer (AMS) measurements were conducted for the first time with a novel PM 2.5 (particulate matter with aerodynamic diameter ≤ 2.5 µm) lens in two major cities of China: Xi'an and Beijing. We denote the periods with visibility below 2 km as extreme haze and refer to the rest as reference periods. During the measurements in Xi'an an extreme haze covered the city for about a week and the total non-refractory (NR)-PM 2.5 mass fraction reached peak concentrations of over 1000 µg m −3 . During the measurements in Beijing two extreme haze events occurred, but the temporal extent and the total concentrations reached during these events were lower than in Xi'an. Average PM 2.5 concentrations of 537 ± 146 and 243 ± 47 µg m −3 (including NR species and equivalent black carbon, eBC) were recorded during the extreme haze events in Xi'an and Beijing, respectively. During the reference periods the measured average concentrations were 140 ± 99 µg m −3 in Xi'an and 75 ± 61 µg m −3 in Beijing. The relative composition of the NR-PM 2.5 evolved substantially during the extreme haze periods, with increased contributions of the inorganic components (mostly sulfate and nitrate). Our results suggest that the high relative humidity present during the extreme haze events had a strong effect on the increase of sulfate mass (via aqueous phase oxidation of sulfur dioxide). Another relevant characteristic of the extreme haze is the size of the measured particles. During the extreme haze events, the AMS showed much larger particles, with a volume weighted mode at about 800 to 1000 nm, in contrast to about 400 nm during reference periods. These large particle sizes made the use of the PM 2.5 inlet crucial, especially during the severe haze events, where 39 ± 5 % of the mass would have been lost in the conventional PM 1 (particulate matter with aerodynamic diameter ≤ 1 µm) inlet. A novel positive matrix factorization procedure was developed to apportion the sources of organic aerosols (OA) based on their mass spectra using the multilinear engine (ME-2) controlled via the source finder (SoFi). The procedure allows for an effective exploration of the solution space, a more objective selection of the best solution and an estimation of the rotational uncertainties. Our results clearly show an increase of the oxygenated organic aerosol (OOA) mass during extreme haze events. The contribution of OOA to the Published by Copernicus Publications on behalf of the European Geosciences Union. 3208M. Elser et al.: OA chemical composition and sources during haze events in China total OA increased from the reference to the extreme haze periods from 16.2 ± 1.1 to 31.3 ± 1.5 % in Xi'an and from 15.7 ± 0.7 to 25.0 ± 1.2 % in Beijing. By contrast, during the reference periods the total OA mass was dominated by domestic emissions of primary aerosols from biomass burning in Xi'an (42.2 ± 1.5 % of OA) and coal combustion in Beijing (55.2 ± 1.6 % of OA). These two sources are also mostly responsible for extremely high polycy...

Field characterization of the PM<sub>2.5</sub> Aerosol Chemical Speciation Monitor: insights into the composition, sources, and processes of fine particles in eastern China

“…The recent evaluation of the CV for inorganic species measurements showed overall agreement with those by co-located measurements (Hu et al, 2017b). The PM 2.5 -AMS equipped with a SV was deployed once in China, which provided new insights into composition and sources of PM 2.5 in Beijing and Xi'an (Elser et al, 2016). The results showed that secondary inorganic components (mostly sulfate and nitrate) and oxygenated organic aerosol (OOA) had large enhancements in large sizes (> 1 µm) during the extreme haze periods in Beijing and Xi'an.…”

“…For instance, 91 % of PM 2.5 nitrate was found in NR-PM 1 at an urban background site in Paris, France . Our results indicate that it is of great importance to chemically characterize PM 1−2.5 in China because of its large contribution to the total mass of PM 2.5 in accordance with Elser et al (2016). Figure 4 shows the relationship between the PM 1 / PM 2.5 ratios of the aerosol species from the Q-ACSM measurements and the ratio of SOA / OA in PM 2.5 .…”

“…The aerosol pH and liquid water content (ALWC) associated with inorganic species in PM 1 and PM 2.5 were predicted using the "forward" mode of ISORROPIA-II (Fountoukis and Nenes, 2007), with both inorganic composition and gasphase species (HNO 3 and NH 3 ) as model inputs. To investigate the potential influence of mineral dust and sea salt, as well as the differences of aerosol chemical species measured by different instruments on the pH prediction, the model was also run with and without K + -Ca 2+ -Mg 2+ or Na + -Cl − , respectively.…”

“…The techniques for real-time measurements of inorganic species have been well developed, e.g., the particle-into-liquid sampler -ion chromatography (PILS-IC) (Orsini et al, 2003), Monitor for AeRosols and GAses (MARGA) (Du et al, 2011), and gas and aerosol collectorion chromatography (GAC-IC) , and are also widely used for chemical characterization of PM 2.5 in China. However, real-time measurements of the total organics in PM 2.5 and subsequent OA source apportionment were barely performed in China (Elser et al, 2016). Although ambient organic carbon (OC) and elemental carbon (EC) can be measured semi-continuously, typically in hourly resolution, they can only be used to differentiate primary and secondary OC using the EC-tracer technique (Turpin and Huntzicker, 1995).…”

Indoor terpene emissions from cooking with herbs and pepper and their secondary organic aerosol production potential

“…Both secondary organic aerosol (SOA) and aged NMOGs from terpenes may have deleterious effects on human health710, demonstrating the importance of identifying indoor terpene sources. Cooking processes have been recognized as major contributors to particulate matter (PM) concentrations in indoor11121314 and outdoor1516171819 environments. In addition to PM, these processes have been shown to emit large amounts of NMOGs20212223.…”