Understanding the local sources of atmospheric formaldehyde (HCHO) is a key step in accurately determining the inversion of biogenic volatile organic compounds (BVOCs). This study aims to clarify the ...main sources and emission patterns of local total HCHO column densities over Ethiopia and Kenya. Between 2005 and 2015, the total monthly HCHO varied from 3.7 × 1015 molecules/cm2 to 7.7 × 1015 molecules/cm2. Monthly HCHO showed a strong seasonal pattern with annual peaks on March, July (small peak) and October, which well matched with the rainy seasons in Ethiopia and Kenya. Natural sources contributed 36% to the total HCHO in the study area. Grassland and savannas showed high column densities in the long rainy season starting from March, with the monthly average emission value of 5.6 × 1015 molecules/cm2. Multiple regression result showed that vegetation contributed 3.5 × 1013 molecules/cm2 to monthly HCHO, with grassland and forest in eastern Kenya and the boundary of Ethiopia and Kenya were the main contributors in these regions. Biomass burning and methane contributed to HCHO emission in the western and northern Ethiopia with a magnitude of 1.4 × 1014 molecules/cm2 and 6.2 × 1016 molecules/cm2 per month, respectively. Economic activities showed negative response to HCHO columns, except over the two small-scale regions of Addis Ababa City and Nairobi City. This study quantified the HCHO from various sources and suggested that natural sources produce more HCHO than anthropogenic sources over Ethiopia and Kenya.
•High column densities of HCHO over grassland and savanna areas compared to other land covers.•Natural sources contributed 36% of the total HCHO in western Ethiopia and southern Kenya.•Biomass burning and vegetation was the top HCHO contributor in western Ethiopia and eastern Kenya, respectively.•Economic activities explain the HCHO trend in Addis Ababa City and Nairobi City better than other sources.
Abstract
The Arctic is warming two to three times faster than the global average, and the role of aerosols is not well constrained. Aerosol number concentrations can be very low in remote ...environments, rendering local cloud radiative properties highly sensitive to available aerosol. The composition and sources of the climate-relevant aerosols, affecting Arctic cloud formation and altering their microphysics, remain largely elusive due to a lack of harmonized concurrent multi-component, multi-site, and multi-season observations. Here, we present a dataset on the overall chemical composition and seasonal variability of the Arctic total particulate matter (with a size cut at 10
μ
m, PM
10
, or without any size cut) at eight observatories representing all Arctic sectors. Our holistic observational approach includes the Russian Arctic, a significant emission source area with less dedicated aerosol monitoring, and extends beyond the more traditionally studied summer period and black carbon/sulfate or fine-mode pollutants. The major airborne Arctic PM components in terms of dry mass are sea salt, secondary (non-sea-salt, nss) sulfate, and organic aerosol (OA), with minor contributions from elemental carbon (EC) and ammonium. We observe substantial spatiotemporal variability in component ratios, such as EC/OA, ammonium/nss-sulfate and OA/nss-sulfate, and fractional contributions to PM. When combined with component-specific back-trajectory analysis to identify marine or terrestrial origins, as well as the companion study by Moschos
et al
2022
Nat. Geosci.
focusing on OA, the composition analysis provides policy-guiding observational insights into sector-based differences in natural and anthropogenic Arctic aerosol sources. In this regard, we first reveal major source regions of inner-Arctic sea salt, biogenic sulfate, and natural organics, and highlight an underappreciated wintertime source of primary carbonaceous aerosols (EC and OA) in West Siberia, potentially associated with the oil and gas sector. The presented dataset can assist in reducing uncertainties in modelling pan-Arctic aerosol-climate interactions, as the major contributors to yearly aerosol mass can be constrained. These models can then be used to predict the future evolution of individual inner-Arctic atmospheric PM components in light of current and emerging pollution mitigation measures and improved region-specific emission inventories.
An in situ method for studying gas-phase C2–C7 monocarboxylic volatile organic acids (VOAs) in ambient air was developed and evaluated. Samples were collected directly into the cold trap of the ...thermal desorption unit (TD) and analysed in situ using a gas chromatograph (GC) coupled to a mass spectrometer (MS). A polyethylene glycol column was used for separating the acids. The method was validated in the laboratory and tested on the ambient air of a boreal forest in June 2015. Recoveries of VOAs from fluorinated ethylene propylene (FEP) and heated stainless steel inlets ranged from 83 to 123 %. Different VOAs were fully desorbed from the cold trap and well separated in the chromatograms. Detection limits varied between 1 and 130 pptv and total uncertainty of the method at mean ambient mixing ratios was between 16 and 76 %. All straight chain VOAs except heptanoic acid in the ambient air measurements were found with mixing ratios above the detection limits. The highest mixing ratios were found for acetic acid and the highest relative variations for hexanoic acid. In addition, mixing ratios of acetic and propanoic acids measured by the novel GC-MS method were compared with proton-mass-transfer time-of-flight mass spectrometer (PTR-TOFMS) data. Both instruments showed similar variations, but differences in the mixing ratio levels were significant.
Polycyclic aromatic hydrocarbons (PAH compounds) were measured in the PM
10 fraction from ambient air at Virolahti, Finland. The sampling site is located in a rural area in the south-eastern corner ...of Finland, near the Russian border. Altogether, 51 daily and 85 weekly filter samples were collected in 2007–2008. The yearly average concentration of benzo(a)pyrene at Virolahti in 2007 was 0.21 ng m
−3, which is well below the annual target value of 1 ng m
−3 set by the European Union. The positive matrix factorization (PMF) method was applied in source apportionment for daily PAH data combined with other pollutant data. A three-factor solution of the PMF analysis with 28 components was chosen. These three factors were identified as long-range transported secondary particles (F1), combustion (F2) and a sea-salt factor (F3). The conditional probability function (CPF) was used to combine wind direction sectors with the PMF factors. In cases F1 and F2, pollutants mainly originated from the south-east, whereas pollutants in F3 came from the south-western sector.
PAHs entered into the combustion factor 2 together with SO
2, NO
x, black carbon and potassium. This suggests that the PAHs at Virolahti originated from traffic and industrial pollution, as well as biomass burning. Elevated concentrations occurred throughout the winter period and most frequently originated from the south-eastern sector between 90°–135°. This sector includes, among other transboundary areas, the metropolis of St. Petersburg at a distance of 160 km.
► PAHs in PM10 were collected at Virolahti, Finland. ► Benzo(a)pyrene was relatively high compared to other European background sites. ► PMF method was applied for daily PAH data combined with other pollutant data. ► Major source area of PAHs was in the eastern sector.
Published biogenic volatile organic compound (BVOC) emission rates of Norway spruces vary a lot. In this study we combined published Norway spruce emission rates measured in boreal forests and added ...our new, unpublished emission data from Southern (SF) and Northern Finland (NF). Standardized summer monthly mean emission potentials of isoprene vary from below the detection limit to 7 μg g
–1
(dw)
h
–1
, and monoterpene (MT) and sesquiterpene (SQT) emission potentials 0.01–3 μg g
–1
(dw)
h
–1
and 0.03–2.7 μg g
–1
(dw)
h
–1
, respectively. In this study, we found much higher SQT emissions from Norway spruces than previously measured, and on average SQTs had higher emission potentials than isoprene or MTs. The highest monthly mean SQT emission potential of 13.6 μg g
–1
(dw)
h
–1
was observed in September in Southern Finland. We found that none of the younger (33–40 years) trees in Hyytiälä, Southern Finland, emitted isoprene, while one 50-year-old tree was a strong isoprene emitter. The difference due to age could not be confirmed, since all measured small trees were growing in Hyytiälä, so this could also be due to the same genetic origin. On average, older trees (>80 years) emitted about ten times more isoprene and MTs than younger ones (<80 years), but no clear difference was seen in SQT emissions. SQT emissions can be more related to stress effects. As shown here for Norway spruce, it is possible that the emission factor of SQTs is significantly higher than what is currently used in models, which may have significant effects on the prediction of formation and growth of new particles, since the secondary organic aerosol (SOA) formation potential of SQTs is high, and this may have significant effects on the formation and growth of new particles. Due to the high secondary organic aerosol (SOA) formation potentials of SQTs, the impact on SOA formation and mass could be even higher.
The monoterpene, isoprene, and light hydrocarbon emission rates of tea-leafed willow (
Salix phylicifolia), aspen (
Populus tremula), and silver birch (
Betula pendula) were measured during the ...growing season 1996 in the boreal vegetation zone using a dynamic flow-through technique. All tree species had significant (2.8–10
μg
g (dry weight)
-1
h
-1) monoterpene emission rates when leaves were young in May. In addition, willow emitted 1-butene, ethene, and propene when it was blooming in May. In August, silver birch emitted monoterpenes (6–12
μg
g (dry weight)
-1
h
-1). Then the main species emitted were ocimenes and sabinene. Birch emitted only minor amounts of isoprene. Willow and aspen are high isoprene emitters (up to 76
μg
g (dry weight)
-1
h
-1 in August). Isoprene emissions began 2–3 weeks after onset of leafing. The phenological state was estimated using the effective temperature sum. Isoprene synthase began when the effective temperature sum exceeded 120–210 and 120–280 degree days for willow and aspen, respectively. In addition to phenology, isoprene emissions were dependent on temperature and photosynthetically active radiation while the terpene emissions were dependent on temperature only.
Ambient air concentrations and source contributions of 71 volatile organic compounds (VOCs) including C2-C10 nonmethane hydrocarbons, halogenated hydrocarbons, and carbonyls were studied at urban and ...residential sites in Finland. On the basis of the emission profile and concentration measurements, the contributions of different sources were estimated using a chemical mass balance (CMB) receptor model. It was shown that it is possible to apply CMB in the case of a large number of different compounds with different properties. However, the performance of the model varies significantly for the different compounds. According to the CMB analysis, major sources for these VOCs at the urban site were traffic and distant sources. At the residential site, the contribution due to traffic was minor while distant sources, liquid gasoline, and wood combustion made higher contributions. However, different compound groups or compounds were found to have totally different sources. It was also shown that a biogenic compound, isoprene, also has significant anthropogenic sources and that at some locations wood combustion can be an important source for some VOCs usually considered as traffic-related compounds (e.g., benzene).
Africa is one of the less studied continents with respect to atmospheric aerosols. Savannahs are complex dynamic systems sensitive to climate and land-use changes, but the interaction of these ...systems with the atmosphere is not well understood. Atmospheric particles, called aerosols, affect the climate on regional and global scales, and are an important factor in air quality. In this study, measurements from a relatively clean savannah environment in South Africa were used to model new particle formation and growth. There already are some combined long-term measurements of trace gas concentrations together with aerosol and meteorological variables available, but to our knowledge this is the first detailed simulation that includes all the main processes relevant to particle formation. The results show that both of the particle formation mechanisms investigated overestimated the dependency of the formation rates on sulphuric acid. From the two particle formation mechanisms tested in this work, the approach that included low volatile organic compounds to the particle formation process was more accurate in describing the nucleation events than the approach that did not. To obtain a reliable estimate of aerosol concentration in simulations for larger scales, nucleation mechanisms would need to include organic compounds, at least in southern Africa. This work is the first step in developing a more comprehensive new particle formation model applicable to the unique environment in southern Africa. Such a model will assist in better understanding and predicting new particle formation – knowledge which could ultimately be used to mitigate impacts of climate change and air quality.
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