Sources, size-resolved deposition in the human respiratory tract and health risks of submicron black carbon in urban atmosphere in Pearl River Delta, China.

Black carbon (BC) has a significantly negative impact on air quality, climate and human health. Here we investigated the sources and health effects of BC in urban area of the Pearl River Delta (PRD) based on online data measured by Aerodyne soot particle high-resolution time of flight aerosol mass spectrometer (SP-AMS). In urban PRD, BC particles mainly came from vehicle emissions especially heavy-duty vehicle exhausts (contributing 42.9 % of total BC mass concentration), long-range transport (27.6 %), and aged biomass combustion emissions (22.3 %). Indicated by source analysis using simultaneous aethalometer data, BC associated with local secondary oxidation and transport may also be originated from fossil fuel combustion, especially traffic sources in urban and surrounding areas. Size-resolved BC mass concentrations provided by SP-AMS, for the first time to our best knowledge, were used to calculate BC deposition in the human respiratory tract (HRT) of different populations (children, adults, and the elderly) by the Multiple-Path Particle Dosimetry (MPPD) model. We found that submicron BC was deposited more in the pulmonary (P) region (49.0-53.2 % of the total BC deposition dose), while less in the tracheobronchial (TB, 35.6-37.2 %) and head (HA, 11.2-13.8 %) regions. Adults suffered the highest BC deposition (1.19 µg day-1) than the elderly (1.09 µg day-1) and children (0.25 µg day-1). BC deposition rate was greater at night (especially 18:00-24:00) than during the daytime. The maximum deposition in the HRT was found for BC particles around 100 nm, mainly in deeper respiratory regions (TB and P), which may cause more serious health effects. Adults and the elderly group are confronted with the notable carcinogenic risk of BC in the urban PRD, up to 29 times higher than the threshold. Our study emphasizes the need to control BC pollution in the urban area, especially nighttime vehicle emissions.

Chemical composition and sources of amines in PM2.5 in an urban site of PRD, China.

Atmospheric amines have attracted increasing attention due to their significant impact on new particle formation, particle hygroscopicity and particle optical properties. In this study, four low-molecule-weight amines were detected from PM2.5 filter samples collected at an urban site of Pearl River Delta (PRD) region of China in 2018 autumn. During the campaign, the mass concentrations of ambient particulate methylamine (MA, CH3NH2), dimethylamine (DMA, (CH3)2NH), trimethylamine (TMA, (CH3)3N), and diethylamine (DEA, (C2H5)2NH) were quantified at daily or 12-h resolution using an optimized Ion Chromatograph (IC) method. The total measured amine concentration was 297 ± 209 ng/m3, which can account for 0.76 ± 0.33% of PM2.5 mass concentrations. The particulate amines in PRD urban area were dominated by MA (243 ± 179 ng/m3), accounting for over 80% of total amines, then followed by DMA (49 ± 30 ng/m3, 16.5%), TMA (4 ± 2 ng/m3) and DEA (1 ± 1 ng/m3). Based on the correlation analysis, MA and DMA mainly presented as nitrate and sulfate salts. We speculate the amines tend to react with gas-phase HNO3 or particle-phase nitrate to form particulate amine salts via local process in Guangzhou. As the relative humidity (RH) increased, enhanced partitioning of amine towards the particle phase was observed. Using approach of multiple linear regression, 71% of the particulate amines in PRD urban site could be explained by acid-base process and the rest by primary emissions from combustion sources (29%).

Tower-based measurements of NMHCs and OVOCs in the Pearl River Delta: Vertical distribution, source analysis and chemical reactivity.

Measurements of vertical distribution of volatile organic compounds (VOCs) have attracted wide attentions, which could help to understand atmospheric oxidation mechanism and provide implications for VOC control. This study measured the non-methane hydrocarbons (NMHCs) and oxygenated VOCs (OVOCs) simultaneously for the first time at three different heights, namely ground, 118 m and 488 m, in the Canton Tower located in the urban core of the Pearl River Delta (PRD). The results show that NMHCs decreased while some OVOC species such as formaldehyde and acetaldehyde increased with increasing height. It was mainly attributed to the dilution and chemical loss of NMHCs but secondary production of OVOCs during vertical transport. Ratio analysis and receptor modeling indicate that vehicle exhausts (47%) and fuel evaporation (39%) were major sources of the total NMHCs. Interestingly, industry contributed much more at 118 m, probably affected by organic gas discharge from the high chimney of industrial factories. The chemical reactivities in terms of OH radical loss rate (LOH), ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) were lowest at 118 m, smaller than those influenced by high fresh NMHC emissions at ground and strong formation of secondary species (e.g. OVOCs) at 488 m. OH exposure estimated by isoprene and m,p-xylene/ethylbenzene was different depending on their time scale of vertical turbulent mixing and chemical loss. OVOC species measured at different heights were positively correlated with Ox (R = 0.48-0.87), indicating that OVOCs were largely contributed by secondary formation in photochemical process. The tower measurements of NMHCs and OVOCs provided a unique opportunity to investigate the VOC distribution and chemical behaviors, which could give important information for understanding O3 and PM2.5 pollution mechanism in the PRD region with fast developing urban setting and substantially changing air quality.

[Vertical Distribution of Surface Formaldehyde in the Pearl River Delta Urban Area Based on Observations at the Canton Tower].

To investigate the vertical distribution of atmospheric formaldehyde in the Pearl River Delta (PRD) urban area, simultaneous measurements were performed at three heights on Canton Tower for the first time. Carbonyls including formaldehyde were sampled with 2,4-dinitrophenylhydrazin (DNPH) at noon for 32 days in autumn of 2018, and then analyzed using high-performance liquid chromatography (HPLC). Average mass concentrations of formaldehyde at ground level, 118 m, and 488 m sites at Canton Tower were (5.10±1.93), (6.61±2.84), and (5.33±2.55) µg·m-3, respectively. The measured formaldehyde was positively correlated with atmospheric oxidant Ox at the three sites (R 0.65-0.75), indicating that photochemical formation is an important source for urban formaldehyde in PRD. Three different profiles were found for formaldehyde vertical distribution during the measurements. The most frequently observed one showed a higher value at 118 m while lower ones at ground level and 488 m, occurring when the boundary layer is in moderate convection state with high photochemical reactivity. The 118 m layer may be also influenced by transported high-chimney emissions from industries in suburban areas. Vertical columns of formaldehyde were also calculated according to its vertical profile. The average value was (11.23±4.80)×1015 molecules·cm-2, 19% lower than that from satellite retrieval, while in the same magnitude as values reported in reference papers.

Deriving emission fluxes of volatile organic compounds from tower observation in the Pearl River Delta, China.

Accurate estimation of speciated emissions of volatile organic compounds (VOCs) is challenging due to the complexity of both species and sources. Evaluation of the bottom-up emission inventory (EI) by atmospheric observation is needed to better understand the VOC emissions and then to control air pollutions caused by VOCs. This study conducts vertical measurements of VOCs between November 3 and 11, 2018 at the Canton Tower in the urban core of Pearl River Delta (PRD), China. A mixed layer gradient (MLG) technique is applied to the tower observation data to derive emission fluxes for individual VOC. The results show that the measured VOCs concentrations at ground level were always higher than those at the heights of 118 m and 488 m. Obvious vertical gradients of concentrations were found for VOC species, such as benzene, toluene and isoprene. The emission flux was estimated to be largest for propane (3.29 mg m-2 h-1), followed by toluene (2.55 mg m-2 h-1), isoprene (2.24 mg m-2 h-1), n-butane (2.10 mg m-2 h-1) and iso-pentane (1.73 mg m-2 h-1). The total VOC emission fluxes were around 3 times larger than those in the EI, suggesting 1.5-2 times underestimations of ozone formation potential (OFP) and secondary organic aerosol potential (SOAP) by current EI. Substantial underestimations (3-20 times) were found for C2-C5 alkanes by current EI. Due to unmeasured input parameters, limited sample size and short sampling period, there are still large uncertainties (40%-117%) in the estimated emission fluxes for individual species. Whereas, this study shows that the tower observation and emission estimation using MLG method could provide useful information for better understanding vertical distributions and emission fluxes of VOCs, and pioneer in assessing the existing emission inventories at species-level and hour-level.