Dry deposition study by using dry deposition plate and water surface sampler in Shalu, central Taiwan

Urban air PCDD/Fs: Dry deposition fluxes and mass transfer coefficients determined using a water surface sampler

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) cause significant environmental concerns. Atmospheric PCDD/Fs permeate water bodies and other ecosystems through wet and dry deposition. In an urban site, dry deposition flux samples of gaseous phase PCDD/Fs were collected by a water surface sampler (WSS) operated between June 2022 and June 2023. There is a conspicuous absence of literature on the direct measurement of dry deposition flux levels in the gaseous phase of PCDD/Fs. In the study, PCDD/Fs in the gas phase reaching the WSS dissolved in the water according to Henry's Law. The PCDD/Fs in the water were transferred to an XAD-2 resin column, sorbing the dissolved PCDD/Fs. The average monthly gas phase dry deposition flux was 34.07 ± 9.35 pg/m2-day (7.35 ± 2.16 pg I-TEQ/m2-day). The highest flux was measured in March (49.53 pg/m2-day), and the lowest was in August (18.64 pg/m2-day). These values indicated the direct flux from air to water. The atmospheric concentration of the gas-phase ranged from 68.38 to 126.88 fg/m3 (13.22-25.01 fg I-TEQ/m3). Dry deposition fluxes and concentrations of atmospheric PCDD/Fs were bigger in the colder months than in the warmer months. This was probably due to a significant increase in residential heating during the colder months, decreased photochemical reactions, and lower mixing heights. Regarding congeners in the dry deposition flux and concentration values in I-TEQ units, 2,3,7,8-TCDD compound predominated with the proportions of 31.61 ± 7.76% and 29.09 ± 12.34%, respectively. Concurrently measured dry deposition flux (Fg) and ambient air concentration (Cg) of PCDD/Fs were considered in the determination of mass transfer coefficient (MTC = Fg/Cg) calculation for each PCDD/F congener. The average MTC for targeted 17 PCDD/Fs was 0.45 ± 0.15 cm/s, and it fluctuated between 0.89 ± 0.30 cm/s for 2,3,7,8-TCDF and 0.2 ± 0.16 cm/s for OCDD.

Chemical Composition and Deposition Fluxes of Water-Soluble Inorganic Ions on Dry and Wet Deposition Samples in Wuhan, China

Measurement of PM_2.5 concentration, dry and wet deposition of water-soluble inorganic ions (WSII) and their deposition flux was carried out. During sampling, a total number of 31 samples of PM_2.5, five wet deposition samples and seven dry deposition samples were collected. The analyses results showed that the average concentration of PM_2.5 was 122.95 µg/m³ whilst that of WSII was 51.63 µg/m³, equivalent to 42% of the total mass of PM_2.5. The correlation coefficients between WSII in samples of PM_2.5 was significant (r = 0.50 and p-value of 0.0019). Ions of   SO 4 2 - , NO 3 - , Cl - , and   NH 4 + were dominant in the entire samples (PM_2.5, dry and wet depositions), nevertheless, the average concentration of both SO 4 2 - and Cl - were below the China environmental quality standard for surface water. The ratio of dominant anions in wet deposition ( SO 4 2 - / NO 3 - ) was 1.59, whilst that for dry deposition ( SO 4 2 - / Cl - ) was 1.4, indicating that acidity was mainly derived from sulphate. In the case of dominant cations, the dry and wet deposition ratios ( Ca 2 + / NH 4 + ) were 1.36 and 1.37, respectively, suggesting the alkaline substances were mainly dominated by calcium salts. Days with higher recorded concentrations of PM_2.5 were accompanied by dry and warm boundary layer structure, weak low-level wind and strong inversion layer.

Source apportionment of settleable particles in an impacted urban and industrialized region in Brazil

Settleable particulate matter (SPM), especially coarser particles with diameters greater than 10 μm, has been found culprit of high deposition rates in cities affected by hinterland industrial activities. This is the case of Metropolitan Region of Vitoria (MRV), Espirito Santo, Brazil where industrial facilities are located within the urban sprawl and building constructions are intense. Frequent population complaints to the environmental protection agency (IEMA) throughout the years have triggered monitoring campaigns to determine SPM deposition rates and source apportionment. Eight different locations were monitored throughout the MRV, and SPM was quantified and chemically characterized. Sources profiles were defined either by using US EPA SPECIATE data or by experimental analysis. Atmospheric fallout in the MRV ranged between 2 and 20g/(m² 30-day), with only one monitoring station ranging from 6-10 g/(m² 30-day). EC, OC, Fe, Al, and Si were found the main constituents of dry deposition in the region. Source apportionment by the chemical mass balance (CMB) model determined that steel and iron ore pelletizing industries were the main contributor to one of the eight locations whereas resuspension, civil construction, and vehicular sources were also very important contributors to the other stations. Quarries and soil were also considered expressive SPM sources, but at the city periphery. CMB model could differentiate contributions from six industrial source groups: thermoelectric; iron ore, pellet, and pellet furnaces; coal coke and coke oven; sintering, blast furnace, and basic oxygen furnace; and soil, resuspension, and vehicles. However, the CMB model was unable to differentiate between iron ore and pellet stockpiles which are present in both steel and iron ore pelletizing industries. Further characterization of source and SPM might be necessary to aid local authorities in decision-making regarding these two industrial sources.

Atmospheric particle dry deposition of major ions to the South Atlantic coastal area observed at Baía de Todos os Santos, Brazil

The coastal atmosphere adjacent to large urban areas can be strongly affected by the emission of air pollutants, among them, major ions species. In this study, the chemical composition and sources of carboxylates and other water-soluble ions in fine and coarse aerosols as well as estimates of particle dry deposition fluxes were studied at a tropical coastal site affected by an urban environment. The mean concentrations of the total carboxylates were 78 ng m–3 in fine fraction and 81 ng m–3 in coarse fraction of particulate matter (PM). The corresponding values for the total inorganic ions were 2143 ng m–3 and 4880 ng m–3 respectively. Main sources for fine particles were: (i) photochemical formation of carboxylic acids in vapor phase and a posterior gas-to-particle conversion onto sea salt particles; (ii) emissions from anthropic sources with long range transportation processes; and (iii) the interchanging of volatile species among atmospheric phases. In turn, for coarse particles, the predominant sources were: (i) gas-phase species and ab/adsorbed onto pre-existing particles afterwards; (ii) primary emission of coarse particles from anthropogenic sources; and (iii) sea salt spray and/or soil resuspension. Finally, particle dry deposition was a very important mechanism representing air-to-sea fluxes of major species.

Design and validation of a passive deposition sampler

A new, passive particle deposition air sampler, called the Einstein-Lioy Deposition Sampler (ELDS), has been developed to fill a gap in passive sampling for near-field particle emissions. The sampler can be configured in several ways: with a protective hood for outdoor sampling, without a protective hood, and as a dust plate. In addition, there is an XRF-ready option that allows for direct sampling onto a filter-mounted XRF cartridge which can be used in conjunction with all configurations. A wind tunnel was designed and constructed to test the performance of different sampler configurations using a test dust with a known particle size distribution. The sampler configurations were also tested versus each other to evaluate whether or not the protective hood would affect the collected particle size distribution. A field study was conducted to test the sampler under actual environmental conditions and to evaluate its ability to collect samples for chemical analysis. Individual experiments for each configuration demonstrated precision of the sampler. The field experiment demonstrated the ability of the sampler to both collect mass and allow for the measurement of an environmental contaminant i.e. Cr(6+). The ELDS was demonstrated to be statistically not different for Hooded and Non-Hooded models, compared to each other and the test dust; thus, it can be used indoors and outdoors in a variety of configurations to suit the user's needs.

Dry deposition of Mn, Zn, Cr, Cu and Pb in particles of sizes of 3 μm, 5.6 μm and 10 μm in central Taiwan

This investigates the concentrations of Mn, Zn, Cr, Cu, and Pb ambient air in total suspended particulates (TSPs) and dry deposition. The ratios of the calculated to measured dry deposition fluxes of ambient-air Mn, Zn, Cr, Cu and Pb at five characteristic sampling sites from 2009 to 2010 were determined using two dry deposition models. Experimental results demonstrate that the mean concentrations of metallic elements in TSPs and dry deposition were highest at the Quan-xing (industrial) sampling site, which is surrounded by various industrial factories and is in a severely polluted area. The mean seasonal concentrations of metallic elements in TSPs were highest in the winter and fall at all five sites. The analytical concentrations of metallic elements in fall and winter at these five sites were elevated in low winds. The Baklanov model yielded more accurate predictions concerning the dry deposition of metallic elements in ambient air when the sizes of the deposited particles were <5.6 μm, and the Noll and Fang model yielded better predictions when the sizes of the particles were >5.6 μm.