Temporal variations of atmospheric carbonyls in urban ambient air and street canyons of a Mountainous city in Southwest China

Carbonyl compounds in urban ambient air and street canyons were measured from December 2008 to August 2009 in a mountainous city in southwest China (Guiyang). The formaldehyde yield from the photo-oxidation of isoprene emitted by vegetation was estimated to be in the range of 0.63–3.62 μg m^?3 from May to August, which accounted for 28.8–33.4% of ambient formaldehyde. Based on the calculation of photolysis rates and rates of reaction with the OH radical, it was found that photolysis was the predominant sink for formaldehyde and acetone in both summer and winter. For acetaldehyde, photo-oxidation by OH radicals and photolysis were the major sinks in summer while photo-oxidation by OH radicals was the dominant sink in winter. Wet precipitation was found to be an important removal process for the atmospheric carbonyls. In the urban ambient air, the average concentrations of formaldehyde, acetaldehyde, acetone and all carbonyls were 4.8 ± 2.1, 5.7 ± 3.3, 5.1 ± 2.5, and 25.1 ± 9.2 μg m^?3 (n = 139), respectively. The average concentrations of these species in street canyons were 18.8 ± 6.5, 9.4 ± 3.2, 10.9 ± 2.1, and 64.1 ± 16.3 μg m^?3 (n = 62), respectively. The significantly higher carbonyl levels on weekdays (compared to weekends) highlight the contribution of vehicle emissions to carbonyls in the street canyons.     

A PLP–LIF kinetic study of the atmospheric reactivity of a series of C4–C7 saturated and unsaturated aliphatic aldehydes with OH

Absolute rate coefficients for the reaction of OH radical with a series of saturated and unsaturated aliphatic aldehydes were measured with the pulsed laser photolysis/laser-induced fluorescence technique at room temperature and as a function of total pressure (p_T=100–400 Torr). No pressure dependence of the rate coefficients was observed. The weighted average values obtained, k_OH±2σ, in units of 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, were 2.88±0.26 for n-butanal, 2.48±0.24 for n-pentanal, 2.60±0.21 for n-hexanal, 2.96±0.23 for n-heptanal, 3.51±0.71 for crotonaldehyde, 2.35±0.32 for trans-2-pentenal, 2.95±0.45 for trans-2-hexenal and 2.45±0.30 for trans-2-heptenal, respectively. The results are compared with previous data when available and with the corresponding coefficients for the reactions with NO₃ and O₃. The dominant tropospheric chemical loss process for these aliphatic aldehydes is the daytime reaction with OH, except in the case of trans-2-heptenal where the estimated lifetime for the reaction with NO₃ radical is smaller than the corresponding value for the OH reaction.     

Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel

Simultaneous measurements of nitrous acid (HONO) and nitrogen dioxide (NO₂) using a differential optical absorption spectroscopy system, nitrogen oxide (NO) by an in situ chemiluminescence analyser and carbon dioxide (CO₂) by a gas chromatographic technique were carried out in the Wuppertal Kiesbergtunnel. At high traffic density HONO concentrations of up to 45 ppbV were observed. However, at low traffic density unexpectedly high HONO concentrations of up to 10 ppbV were measured caused by heterogeneous HONO formation on the tunnel walls. In addition to the tunnel campaigns, emission measurements of HONO, NO₂, NO and CO₂ from different single vehicles (a truck, a diesel and a gasoline passenger car) were also performed. For the correction of the HONO emission data, the heterogeneous HONO formation on the tunnel walls was quantified by two different approaches (a) in different NO₂ emission experiments in the tunnel without traffic and (b) on tunnel wall residue in the laboratory. The HONO concentration corrected for heterogeneous formation on the tunnel walls, in relation to the CO₂ concentration can be used to estimate the amount of HONO, which is directly emitted from the vehicle fleet. From the measured data, emission ratios (e.g. HONO/NO_x) and emission indices (e.g. mg HONO kg⁻¹ fuel) were calculated. The calculated emission index of 88±18 mg HONO kg⁻¹ fuel allows an estimation of the HONO emission rates from traffic into the atmosphere. Furthermore, the heterogeneous formation of HONO from NO₂ on freshly emitted exhaust particles is discussed.     

Emission of N2O on pulse–rice crop rotation in upland

The Seasonally Integrated Flux (SIF) of N₂O emission during pulse cultivation in Rabi season (Season-I: December to April) in rain-fed uplands of Orissa, was found to be 17.7 ± 0.07, 18.7 ± 0.16 and 43.3 ± 0.14 gha^?1 for horse gram (HG), black gram (BG) and green gram (GG) respectively. During the subsequent Rabi season (Season-II), the SIF of N₂O for BG and GG cultivated in the same fields were 20.9 ± 0.24 and 38.0 ± 0.42 gha^?1 respectively. Similarly SIF values during rice cultivation with different cultivars have also been calculated to be in the range ?20.05 ± 0.33 to 21.98 ± 0.29. Statistical analysis showed good correlation of N₂O emission with climatic and soil parameters like temperature, nutrient N and organic matter in soil during pulse cultivation. Multivariate analysis was carried out to factorize the results obtained. Using student ‘t’ test, the N₂O emission was observed to be similar for two consecutive Rabi seasons for pulses like BG and GG.     

Mobile sources of atmospheric polycyclic aromatic hydrocarbons in a roadway tunnel

Amounts of polycyclic aromatic hydrocarbons (PAHs) and oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) in samples collected from the air, from the dust on a guardrail, and from the soils on a tunnel roadway at five sampling sites in a regular roadway tunnel were chemically analyzed in order to determine their sources. Among the 23 PAHs found in the air samples, pyrene was found in the highest concentration (43±7.2 ng/m³), followed by fluoranthene (26±4.3 ng/m³). Among 20 oxy-PAHs found in the air samples, anthraquinone was found in the greatest amount (56±3.9 ng/m³). The average concentration of the major PAHs found in the guardrail dust samples were 6.9±0.77 μg/g for pyrene, 5.5±0.76 μg/g for fluoranthene, and 2.6±0.30 μg/g for phenanthrene. The average concentration of the major oxy-PAHs found in the guardrail dust samples were 9.2±3.5 μg/g for anthraquinone and 1.4±0.50 μg/g for 2-methylanthraquinone. The average concentration of the major PAHs found in the soil samples were 1.1±0.31 μg/g for fluoranthene, 0.92±0.21 μg/g for pyrene, and 0.72±0.16 μg/g for phenanthrene. The average concentration of the major oxy-PAHs found in the soil samples were 1.2±0.88 μg/g for anthraquinone, 0.18±0.04 μg/g for 4-biphenylcarboxaldehyde, and 0.13±0.08 μg/g for 2-methylanthraquinone. The BeP ratios calculated from the results suggest that most PAHs found in the samples collected from the roadway tunnel were from automobile exhaust gases.     

Relative rate measurements of reactions of unsaturated alcohols with atomic chlorine as a function of temperature

The kinetics of two structurally similar unsaturated alcohols, 3-butene-2-ol and 2-methyl-3-butene-2-ol (MBO232), with Cl atoms have been investigated for the first time, as a function of temperature using a relative method. As far as we know, the present work also provides the first value for 3-buten-2-ol. The coefficient at room temperature was also obtained for 2-propene-1-ol (allyl alcohol). The reactions were investigated using a 400 L Teflon reaction chamber coupled with gas chromatograph-coupled with flame-ionization detection (GC-FID) detection. The experiments were performed at atmospheric pressure and at temperatures between 256 and 298 K in air or nitrogen as the bath gas. The obtained kinetic data were used to derive the Arrhenius expressions, k_MBO232=(2.83±2.50)×10⁻¹⁴ exp (2670±249)/T, k_3-buten-2-ol=(0.65±1.60)×10⁻¹⁵ exp (3656±695)/T (in units of cm³ molecule⁻¹ s⁻¹). Finally, results and atmospheric implications are discussed and compared with the reactivity with OH and NO₃ radicals.     

Atmospheric degradation of alkylfurans with chlorine atoms: Product and mechanistic study

As part of a study on the oxidation mechanism of heterocyclic aromatic compounds, some aspects of the atmospheric chemistry of several alkyl derivatives of furan have been investigated. The aim of this work was to identify the products of the reactions of chlorine atoms with 2-methylfuran, 2-ethylfuran and 2,5-dimethylfuran. Experiments were performed in two different smog chambers at 296 ± 2 K and 1000 ± 20 mbar of synthetic air. The experimental investigation was carried out using in situ long-path FTIR absorption spectroscopy and both SPME-GC/FID-ECD and SPME-GC/MS as sampling and detection techniques. The major primary products from the addition reaction channel were 4-oxo-2-pentenoyl chloride and formaldehyde for the reactions of 2-methylfuran and 2,5-dimethylfuran; 4-oxo-2-hexenoyl chloride and acetaldehyde for the reaction of 2-ethylfuran and 5-chloro-2(5H)-furanone for the reactions of both 2-methylfuran and 2-ethylfuran. Other minor products were 4-oxo-2-pentenal, 4-oxo-2-hexenal and 3-hexene-2,5-dione for the 2-methylfuran, 2-ethylfuran and 2,5-dimethylfuran reactions, respectively. From the abstraction pathway, HCl, furfural, 2-acetylfuran, 5-methylfurfural, maleic anhydride and 5-hydroxy-2(5H)-furanone were detected. The formation of furfural, 2-acetylfuran and 5-methylfurfural confirmed the H-atom abstraction from the alkyl group of 2-methylfuran, 2-ethylfuran and 2,5-dimethylfuran, respectively. This mechanism was not observed in previous studies with OH and NO₃ radicals. A mechanism is proposed to explain the main reaction products observed. The observed products confirm that addition of Cl atoms to the double bond of the alkylfuran is the dominant reaction pathway.     

Aerosol optical properties of regional background atmosphere in Northeast China

Aerosol optical properties from 2005 to 2008 at the Longfengshan regional background station in Northeast China were measured and analyzed. The annual mean of aerosol optical depth (AOD) at 440 nm for the four years was about 0.27 ± 0.25, 0.39 ± 0.37, 0.35 ± 0.34, and 0.38 ± 0.38, respectively, and the corresponding annual mean for the Angstrom exponent between 440 nm and 870 nm was about 1.43 ± 0.48, 1.23 ± 0.37, 1.53 ± 0.47, and 1.55 ± 0.42. The average monthly AOD_440nm showed similar seasonal variation with a maximum in spring and a minimum in autumn. The monthly means of AOD at 440, 675, 870 and 1020 nm increase from the January to March with the maxima about 0.77 ± 0.04, 0.65 ± 0.04, 0.58 ± 0.06, 0.57 ± 0.07, respectively and decrease from September to February with the minima about 0.32 ± 0.12, 0.22 ± 0.09, 0.15 ± 0.08, and 0.13 ± 0.07 in January. The monthly mean of Angstrom exponent shows a minimum in March (0.97 ± 0.52) and a maximum in September (1.66 ± 0.29). Both the AOD and Angstrom exponent presents single peak distributions of occurrence frequencies. The Longfenshan data showed high AODs (>1.00) both clustering in the fine mode growth wing and the coarse mode. Two typical cases under dust and haze conditions showed that the AOD under dusty day decreased from 2.20 to 1.20 and the Angstrom exponent increased from 0.10 to 1.00. On the contrast, the AOD under haze day remained relatively stable about 0.90 and the Angstrom exponent was around 1.40. The 3-day backtrajectory analysis at Longfengshan illustrated that the air-masses near ground on the dust day were from Bohai Sea and passed through Liaodong Peninsula and Northeast plain in China. But the air-masses on 500 m AGL were originated from western Mongolia and crossed Gobi deserts, Otindag Sand Land and Horqin Sand Land in Northeast China. The air-masses at Longfengshan near ground 500 m and 1000 m AGL on the haze days were from North China Region and passed through Northeast Heavy Industrial Base in Northeast China.     

Personal exposures to NO2 in the EXPOLIS-study: relation to residential indoor,outdoor and workplace concentrations in Basel,Helsinki and Prague

Personal exposures, residential indoor, outdoor and workplace levels of nitrogen dioxide (NO₂) were measured for 262 urban adult (25–55 years) participants in three EXPOLIS centres (Basel; Switzerland, Helsinki; Finland, and Prague; Czech Republic) using passive samplers for 48-h sampling periods during 1996–1997. The average residential outdoor and indoor NO₂ levels were lowest in Helsinki (24±12 and 18±11 μg m⁻³, respectively), highest in Prague (61±20 and 43±23 μg m⁻³), with Basel in between (36±13 and 27±13 μg m⁻³). Average workplace NO₂ levels, however, were highest in Basel (36±24 μg m⁻³), lowest in Helsinki (27±15 μg m⁻³), with Prague in between (30±18 μg m⁻³). A time-weighted microenvironmental exposure model explained 74% of the personal NO₂ exposure variation in all centres and in average 88% of the exposures. Log-linear regression models, using residential outdoor measurements (fixed site monitoring) combined with residential and work characteristics (i.e. work location, using gas appliances and keeping windows open), explained 48% (37%) of the personal NO₂ exposure variation. Regression models based on ambient fixed site concentrations alone explained only 11–19% of personal NO₂ exposure variation. Thus, ambient fixed site monitoring alone was a poor predictor for personal NO₂ exposure variation, but adding personal questionnaire information can significantly improve the predicting power.     

Kinetics of the gas-phase reactions of NO3 radicals with ethyl acrylate,n-butyl acrylate,methyl methacrylate and ethyl methacrylate

The relative rate method has been used to determine the rate constants for the gas-phase reactions of NO₃ radicals with a series of acrylate esters: ethyl acrylate (k₁), n-butyl acrylate (k₂), methyl methacrylate (k₃) and ethyl methacrylate (k₄) at 298 ± 1 K and 760 Torr. The obtained rate constants are k₁ = (1.8 ± 0.25) × 10^?16 cm³ molecule^?1 s^?1, k₂ = (2.1 ± 0.33) × 10^?16 cm³ molecule^?1 s^?1, k₃ = (3.6 ± 1.2) × 10^?15 cm³ molecule^?1 s^?1, k₄ = (4.9 ± 1.7) × 10^?15 cm³ molecule^?1 s^?1. The experimental rate constants are in good agreement with theoretical rate constants calculated by an algorithm of the correlation between the rate constants and the orbital energies for the reactions of unsaturated VOCs with NO₃ radicals. In addition, the atmospheric lifetimes of the compound against NO₃ attack are estimated and the results show that NO₃ reactions contribute little to the atmospheric losses of acrylate esters except in polluted regions.     

FT-IR kinetic and product study of the Br-radical initiated oxidation of α, β-unsaturated organic carbonyl compounds

Using the relative kinetic technique the kinetics of the gas-phase reactions of Br radicals with acrolein, methacrolein and methylvinyl ketone have been investigated at (301±3) K in 1013 mbar of (N₂+O₂) bath gas at varying proportions. In 1013 mbar of synthetic air the following rate coefficients have been obtained (in units of cm³ molecule⁻¹ s⁻¹): acrolein (3.21±0.11)×10⁻¹²; methacrolein (2.33±0.08)×10⁻¹¹; methyl vinyl ketone (1.87±0.06)×10⁻¹¹. This study represents the first determination of the rate coefficients for these compounds. As for other unsaturated hydrocarbons the rate coefficient with Br was found to increase with increasing partial pressure of O₂. From the product studies of the reactions it has been established that addition of Br radicals to the terminal C-atom is the major pathway in all three cases. However, for acrolein H atom abstraction from the -CO–H group is also significant. Mechanisms are proposed to explain the observed products, mainly β-brominated carbonyl compounds.     

Water-soluble organic nitrogen (WSON) in size-segregated atmospheric particles over the Eastern Mediterranean

Atmospheric water-soluble organic nitrogen (WSON) was determined on size-segregated aerosol particles collected during a two years period (2005–2006) in a remote marine location in the Eastern Mediterranean (Finokalia, Crete island). Average concentration of WSON was 5.5 ± 3.9 nmol m^?3 and 11.6 ± 14.0 nmol m^?3 for coarse (PM_1.3-10) and fine (PM_1.3) mode respectively, corresponding to 13% of Total Dissolved Nitrogen (TDN) in both modes. Air masses origin and correlation with tracers of natural and anthropogenic sources indicate that combustion process (biomass burning and fossil fuel) and African dust play an important role in regulating levels of WSON in both coarse and fine aerosol fractions. Chemical speciation of organic nitrogen pool was attempted by analyzing 47 fine aerosol samples (PM₁) for 17 free amino acids (N-FAA), dimethylamine (DMA) and trimethylamine (TMA). The average concentration of N-FAA was 0.5 ± 0.5 nmol m^?3, while the average concentration of DMA was 0.2 ± 0.8 nmol m^?3, TMA was below detection limit. The percentage contribution of N-FAA and DMA to WSON was 2.1 ± 2.3% and 0.9 ± 3.4%, respectively.     

Aerosol optical properties based on ground measurements over the Chinese Yangtze Delta Region

The characteristics of Aerosol Optical Depth (AOD) and Angstrom exponent were analyzed and compared using Cimel sunphotometer data from 2007 to 2008 at five sites located in the Yangtze River Delta region of China. The simultaneous measurements between Lin’an and ZFU showed a very high consistency of AOD at all wavelengths. The differences are less than 0.02 for Angstrom exponent and AOD at all wavelengths. The mean values of AOD at 440 nm at the Pudong, Taihu and Lin’an were about 0.74 ± 0.43, 0.85 ± 0.46, and 0.89 ± 0.46, respectively. The mean values of Angstrom exponents were about 1.27 ± 0.30, 1.20 ± 0.28 and 1.32 ± 0.35, respectively. The variation of monthly averaged AOD over Pudong showed a single peak distribution, with the maximum value occurring in July (AOD_440nm 1.26 ± 0.61) and minimum in January (AOD_440nm 0.50 ± 0.27). However, the variations of monthly averaged AOD at Taihu and Lin’an showed a bi-modal distribution. There were peak values of AOD occurring in July (AOD_440nm 1.41 ± 0.49) and September (AOD_440nm 1.22 ± 0.52) for Taihu. For Lin’an, the two peak values of AOD occurred in June (AOD_440nm 1.17 ± 0.69) and September (AOD_440nm 1.28 ± 0.46). The AOD accumulated mainly between 0.30–0.90(68%), 0.30–1.20(75%) and 0.30–1.20 (～75%) at Pudong, Taihu, and Lin’an, respectively. The Angstrom exponent accumulated mainly between 1.10–1.60 (75%), 1.10–1.50 (63%) and 1.20–1.60, 50% (50%) at Pudong, Taihu, and Lin’an, respectively.The synchronized observation showed that the AOD at Pudong was larger than those at Dongtan by 0.03, 0.03, 0.04, 0.07, and 0.08 at wavelengths of 1020 nm, 870 nm, 670 nm, 500 nm and 440 nm, respectively. The synchronized observations at Pudong, Taihu and Lin’an showed that the three stations had high level AOD with means at 440 nm about 0.68, 0.73, and 0.78, respectively. The relationship between MODIS retrieved and ground-based measured AOD shows good agreement with R² ranging from 0.68 to 0.79 at Pudong, Taihu, Lin’an and Dongtan. The MODIS results were overestimated comparing the ground measurements at Pudong, Taihu, and Dongtan but exceptional at Lin’an.The analysis results between aerosol optical properties and wind measurement at Pudong showed that the wind speed from the east correlates with the lower observed AOD. The back trajectory analysis indicates that more than 50% airmasses were from the marine area at Pudong, while back trajectories distribution is relatively homogeneous at Lin’an.     

Comparing the desorption and biodegradation of low concentrations of phenanthrene sorbed to activated carbon,biochar and compost

Carbonaceous soil amendments are applied to contaminated soils and sediments to strongly sorb hydrophobic organic contaminants (HOCs) and reduce their freely dissolved concentrations. This limits biouptake and toxicity, but also biodegradation. To investigate whether HOCs sorbed to such amendments can be degraded at all, the desorption and biodegradation of low concentrations of ¹⁴C-labelled phenanthrene (?5 μg L^?1) freshly sorbed to suspensions of the pure soil amendments activated carbon (AC), biochar (charcoal) and compost were compared. Firstly, the maximum abiotic desorption of phenanthrene from soil amendment suspensions in water, minimal salts medium (MSM) or tryptic soy broth (TSB) into a dominating silicone sink were measured. Highest fractions remained sorbed to AC (84 ± 2.3%, 87 ± 4.1%, and 53 ± 1.2% for water, MSM and TSB, respectively), followed by charcoal (35 ± 2.2%, 32 ± 1.7%, and 12 ± 0.3%, respectively) and compost (1.3 ± 0.21%, similar for all media). Secondly, the mineralization of phenanthrene sorbed to AC, charcoal and compost by Sphingomonas sp. 10-1 (DSM 12247) was determined. In contrast to the amounts desorbed, phenanthrene mineralization was similar for all the soil amendments at about 56 ± 11% of the initially applied radioactivity. Furthermore, HPLC analyses showed only minor amounts (<5%) of residual phenanthrene remaining in the suspensions, indicating almost complete biodegradation. Fitting the data to a coupled desorption and biodegradation model revealed that desorption did not limit biodegradation for any of the amendments, and that degradation could proceed due to the high numbers of bacteria and/or the production of biosurfactants or biofilms. Therefore, reduced desorption of phenanthrene from AC or charcoal did not inhibit its biodegradation, which implies that under the experimental conditions these amendments can reduce freely dissolved concentration without hindering biodegradation. In contrast, phenanthrene sorbed to compost was fully desorbed and biodegraded.     

Optical and microphysical properties of severe haze and smoke aerosol measured by integrated remote sensing techniques in Gwangju,Korea

Aerosol optical and microphysical parameters from severe haze events observed in October 2005 at Gwangju, Korea (35.10°N, 126.53°E) were determined from the ground using a multi-wavelength Raman lidar, a sunphotometer, and a real-time carbon particle analyzer and from space using satellite retrievals. Two different aerosol types were identified based on the variability of optical characteristics for different air mass conditions. Retrievals of microphysical properties of the haze from the Raman lidar indicated distinct light-absorbing characteristics for different haze aerosols originating from eastern and northern China (haze) and eastern Siberia (forest-fire smoke). The haze transported from the west showed moderately higher absorbing characteristics (SSA = 0.90 ± 0.03, 532 nm) than from the northern direction (SSA = 0.96 ± 0.02). The organic/elemental carbon (OC/EC) ratio varied between 2.5 ± 0.4 and 4.1 ± 0.7.     

Emission factors of PAHs,methoxyphenols, levoglucosan,elemental carbon and organic carbon from simulated wheat and Kentucky bluegrass stubble burns

Emission factors (EFs) of pollutants from post-harvest agricultural burning are required for predicting downwind impacts of smoke and inventorying emissions. EFs of polycyclic aromatic hydrocarbons (PAH), methoxyphenols (MP), levoglucosan (LG), elemental carbon (EC) and organic carbon (OC) from wheat and Kentucky bluegrass (KBG) stubble burning were quantified in a US EPA test burn facility. The PAH and MP EFs for combined solid+gas phases are 17±8.2 mg kg⁻¹ and 79±36 mg kg⁻¹, respectively, for wheat and 21±15 mg kg⁻¹ and 35±24 mg kg⁻¹, respectively, for KBG. LG, particulate EC and artifact-corrected OC EFs are 150±130 mg kg⁻¹, 0.35±0.16 g kg⁻¹ and 1.9±1.1 g kg⁻¹, respectively, for wheat and 350±510 mg kg⁻¹, 0.63±0.056 g kg⁻¹ and 6.9±0.85 g kg⁻¹, respectively, for KBG. Positive artifacts associated with OC sampling were evaluated and remedied with a two-filter system. EC and OC accounted for almost two-thirds of PM_2.5 mass, while LG accounted for just under 3% of the PM_2.5 mass. Since EFs of these pollutants generally decreased with increasing combustion efficiency (CE), identifying and implementing methods of increasing the CEs of burns would help reduce their emissions from agricultural field burning. PAH, OC and EC EFs are comparable to other similar studies reported in literature. MP EFs appear dependent on the stubble type and are lower than the EFs for hard and softwoods reported in literature, possibly due to the lower lignin content in wheat and KBG.     

Receptor modeling of source apportionment of Hong Kong aerosols and the implication of urban and regional contribution

Understanding the spatial–temporal variations of source apportionment of PM_2.5 is critical to the effective control of particulate pollution. In this study, two one-year studies of PM_2.5 composition were conducted at three contrasting sites in Hong Kong from November 2000 to October 2001, and from November 2004 to October 2005, respectively. A receptor model, principal component analysis (PCA) with absolute principal component scores (APCS) technique, was applied to the PM_2.5 data for the identification and quantification of pollution sources at the rural, urban and roadside sites. The receptor modeling results identified that the major sources of PM_2.5 in Hong Kong were vehicular emissions/road erosion, secondary sulfate, residual oil combustion, soil suspension and sea salt regardless of sampling sites and sampling periods. The secondary sulfate aerosols made the most significant contribution to the PM_2.5 composition at the rural (HT) (44 ± 3%, mean ± 1σ standard error) and urban (TW) (28 ± 2%) sites, followed by vehicular emission (20 ± 3% for HT and 23 ± 4% for TW) and residual oil combustion (17 ± 2% for HT and 19 ± 1% for TW). However, at the roadside site (MK), vehicular emissions especially diesel vehicle emissions were the major source of PM_2.5 composition (33 ± 1% for diesel vehicle plus 18 ± 2% for other vehicles), followed by secondary sulfate aerosols (24 ± 1%). We found that the contribution of residual oil combustion at both urban and rural sites was much higher than that at the roadside site (2 ± 0.4%), perhaps due to the marine vessel activities of the container terminal near the urban site and close distance of pathway for the marine vessels to the rural site. The large contribution of secondary sulfate aerosols at all the three sites reflected the wide influence of regional pollution. With regard to the temporal trend, the contributions of vehicular emission and secondary sulfate to PM_2.5 showed higher autumn and winter values and lower summer levels at all the sites, particularly for the background site, suggesting that the seasonal variation of source apportionment in Hong Kong was mainly affected by the synoptic meteorological conditions and the long-range transport. Analysis of annual patterns indicated that the contribution of vehicular emission at the roadside was significantly reduced from 2000/01 to 2004/05 (p < 0.05, two-tail), especially the diesel vehicular emission (p < 0.001, two-tail). This is likely attributed to the implementation of the vehicular emission control programs with the tightening of diesel fuel contents and vehicular emission standards over these years by the Hong Kong government. In contrast, the contribution of secondary sulfate was remarkably increased from 2001 to 2005 (p < 0.001, two-tail), indicating a significant growth in regional sulfate pollution over the years.     

Aerosol scattering properties in northern China

The aerosol scattering properties were investigated at two continental sites in northern China in 2004. Aerosol light scattering coefficient (σ_sp) at 525 nm, PM₁₀, and aerosol mass scattering efficiencies (α) at Dunhuang had a mean value of 165.1±148.8 M m⁻¹, 157.6±270.0 μg m⁻³, and 2.30±3.41 m² g⁻¹, respectively, while these values at Dongsheng were, respectively, 180.2±151.9 M m⁻¹, 119.0±112.9 μg m⁻³, and 1.87±1.41 m² g⁻¹. There existed a seasonal variability of aerosol scattering properties. In spring, at Dunhuang PM₁₀, σ_sp, and α were 184.1±211.548 μg m⁻³, 126.3±89.6 M m⁻¹, and 1.05±0.97 m² g⁻¹, respectively, and these values at Dongsheng were 146.4±142.1 μg m⁻³, 183.4±81.7 M m⁻¹, and 1.98±1.52 m² g⁻¹, respectively. However, in winter at Dunhuang PM₁₀, σ_sp, and α were 158.1±261.4 μg m⁻³, 303.3±165.2 M m⁻¹, and 3.17±1.93 m² g⁻¹, respectively, and these values at Dongsheng were 155.7±170.1 μg m⁻³, 304.4±158.1 M m⁻¹, and 2.90±1.72 m² g⁻¹, respectively. σ_sp and α in winter were higher than that in spring at both the sites, which coincides with the characteristics of dust aerosol and pollution aerosol. Overall, the dominant aerosol types in spring and winter at both sites in northern China are dust aerosol and pollution aerosol, respectively.     

Measurement of aerosol number size distributions in the Yangtze River delta in China: Formation and growth of particles under polluted conditions

Particle size distribution is important for understanding the sources and effects of atmospheric aerosols. In this paper we present particle number size distributions (10 nm–10 μm) measured at a suburban site in the fast developing Yangtze River Delta (YRD) region (near Shanghai) in summer 2005. The average number concentrations of ultrafine (10–100 nm) particles were 2–3 times higher than those reported in the urban areas of North America and Europe. The number fraction of the ultrafine particles to total particle count was also 20–30% higher. The sharp increases in ultrafine particle number concentrations were frequently observed in late morning, and the particle bursts on 5 of the 12 nucleation event days can be attributed to the homogeneous nucleation leading to new particle formation. The new particle formation events were characterized with a larger number of nucleation-mode particles, larger particle surface area, and larger condensational sink than usually reported in the literature. These suggest an intense production of sulfuric acid from photo-oxidation of sulfur dioxide in the YRD. Overall, the growth rate of newly formed particles was moderate (6.4 ± 1.6 nm h^?1), which was comparable to that reported in the literature.     

Henry’s law constant measurements for formaldehyde and benzaldehyde as a function of temperature and water composition

Henry’s law constants H of formaldehyde and benzaldehyde were determined using a dynamic system based on the water/air equilibrium at the interface within the length of a microporous tube. The measurements were conducted over the range 273–293 K in (i) deionized water, (ii) 35 g L^?1 solution of NaCl simulating seawater and (iii) two nitric acid solutions, i.e. 0.63 and 6.3 wt%.In pure water, the obtained data were used to derive the following Arrhenius expressions: ln H = (6423 ± 542)/T ? (13.4 ± 2.0) and ln H = (6258 ± 280)/T ? (17.5 ± 1.0) for formaldehyde and benzaldehyde, respectively. The H values, calculated at 293 K from Arrhenius expressions cited above were the following (in units of M atm^?1): H = 5020 ± 1170 (formaldehyde), H = 47 ± 5 (benzaldehyde). The temperature dependence of H permits then to derive the solvation enthalpies for both compounds: ΔH_solv = ?(53.4 ± 4.5) kJ mol^?1 and ΔH_solv = ?(52.0 ± 2.3) kJ mol^?1 for formaldehyde and benzaldehyde, respectively.In 35 g L^?1 salt solution, the H values were 27–66% and 12–21% lower than their respective determinations in deionized water, for formaldehyde and benzaldehyde respectively. The observed salt effect was used to estimate the following Setschenow coefficients at 293 K for 0.6 M NaCl: formaldehyde (0.21) and benzaldehyde (0.09).In 6.3 wt% nitric acid solution, H values of benzaldehyde were approximately 30% higher than those found in pure water although no significant influence was observed for formaldehyde.Finally, our experimental data were then used to estimate the fractions of formaldehyde and benzaldehyde in atmospheric aqueous phase and their derived atmospheric lifetimes.