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.     

Drop size-dependent chemical composition of clouds and fogs. Part II: Relevance to interpreting the aerosol/trace gas/fog system

Size-resolved fog drop chemical composition measurements were obtained during a radiation fog campaign near Davis, California in December 1998/January 1999 (reported in Reilly et al., Atmos. Environ. 35(33) (2001) 5717; Moore et al., Atmos. Environ. this issue). Here we explore how knowledge of this size-dependent drop composition—particularly from the newly developed Colorado State University 5-Stage cloud water collector—helps to explain additional observations in the fog environment. Size-resolved aerosol measurements before and after fog events indicate relative depletion of large (>2 μm in diameter) particles during fog accompanied by a relative increase in smaller aerosol particle concentrations. Fog equivalent air concentrations suggest that entrainment of additional particles and in-fog sedimentation contributed to observed changes in the aerosol size distribution. Calculated deposition velocities indicate that sedimentation was an important atmospheric removal mechanism for some species. For example, nitrite typically has a larger net deposition velocity than water and its mass is found preferentially in the largest drops most likely to sediment rapidly. Gas–liquid equilibria in fog for NO₃⁻/HNO₃, NH₄⁺/NH₃, and NO₂⁻/HONO were examined. While these systems appear to be close to equilibrium or relative equilibrium during many time periods, divergences are observed, particularly for low liquid water content (<0.1 g m⁻³) fogs and in different drop sizes. Knowledge of the drop size-dependent composition provided additional data useful to the interpretation of these deviations. The results suggest that data from multi-stage cloud water collectors are useful to understanding fog processes as many depend upon drop size.     

PM2.5 particles and size-segregated ionic species measured during fall season in three urban sites in Korea

Twelve hours integrated fine particles (PM_2.5) and 24-h average size-segregated particles were collected to investigate the chemical characteristics and to determine the size distribution of ionic species during October–December 1999 in three cities of different urban scale; Chongju, Kwangju, and Seoul, Korea. Concentrations of 5-min PM_2.5 black carbon (BC) and hourly criteria air pollutants (PM₁₀, CO, NO_x, SO₂, and O₃) were also measured using the Aethalometer and ambient air monitoring system, respectively.Highest PM_2.5 mass concentrations at Chongju, Kwangju, and Seoul sites were 63.0, 77.9, and 143.7 μg m⁻³, respectively. For the time period when highest PM_2.5 mass occurred, BC level out of PM_2.5 chemical species was highest at both Chongju and Kwangju, and highest NO₃⁻ (23.6 μg m⁻³) followed by BC (23.1 μg m⁻³) were observed at Seoul site, indicating that highest PM_2.5 pollution is closely associated with the traffic emissions. Strong relationships of Fe with BC and Zn at both Kwangju and Seoul sites support that the Fe and Zn measured there are originated partly from same source as BC, i.e. diesel traffics. However, it is suggested that the Fe measured at Chongju is most likely derived from dispersion of soil dust.The size distributions of SO₄²⁻, NO₃⁻, and NH₄⁺ ionic species indicated similar unimodal distributions at all sampling sites. However, different unimodal patterns in the accumulation mode size range with a peak in the smaller size (0.28–0.53 μm, condensation mode) in both Kwangju and Seoul, and in the relatively larger size (0.53–1.0 μm, droplet mode) in Chongju, were found. The potassium ion under the study sites dominates in the fine mode, and its size distribution showed unimodal character with a maximum in the size range 0.56–1.0 μm.     

Annual evolution and generation mechanisms of particulate nitrate in Madrid

During the course of one year (March 2004–March 2005), PM_2.5 particulate nitrate concentrations were semi-continuously measured every 10 min at a Madrid suburban site using the Rupprecht and Patashnick Series 8400N Ambient Particulate Nitrate Monitor (8400N). Gaseous pollutants (NO, NO₂, O₃, HCHO, HNO₂) were simultaneously measured with a DOAS spectrometer (OPSIS AR-500) and complementary meteorological information was obtained by a permanent tower. The particulate nitrate concentrations ranged from the instrumental detection limit of around 0.2 μg m⁻³, up to a maximum of about 25 μg m⁻³. The minimum monthly average was reached during August (0.32 μg m⁻³) and the maximum during November (3.0 μg m⁻³). Due to the semi-volatile nature of ammonium nitrate, peaks were hardly present during summer air pollution episodes. A typical pattern during days with low dispersive conditions was characterized by a steep rise of particulate nitrate in the morning, reaching maximum values between 9 and 14 UTC, followed by a decrease during the evening. On some occasions a light increase was observed at nighttime. During spring episodes, brief diurnal nitrate peaks were recorded, while during the autumn and winter episodes, later and broader nitrate peaks were registered. Analysis of particulate nitrate and related gaseous species indicated the photo-chemical origin of the morning maxima, delayed with respect to NO and closely associated with secondary NO₂ maximum values. The reverse evolution of nitrate and nitrous acid was observed after sunrise, suggesting a major contribution from HNO₂ photolysis to OH formation at this time of the day, which would rapidly produce nitrate in both gaseous and particulate phase. Some nocturnal nitrate maxima appeared under high humidity conditions, and a discussion about their origin involving different possible mechanisms is presented, i.e. the possibility that these nocturnal maximum values could be related to the heterogeneous formation of nitrous and nitric acid by the hydrolysis of NO₂ on wet aerosols.     

Measurements of atmospheric nitrous acid and nitric acid

A highly sensitive technique for the measurement of atmospheric HONO and HNO₃ is reported. The technique is based on aqueous scrubbing using two coil samplers, followed by conversion of HNO₃ to nitrite, derivatization of nitrite to a highly light-absorbing azo dye with sulfanilamide (SA) and N-(1-naphthyl) ethylenediamine (NED), and high performance liquid chromatography (HPLC) analysis. HNO₃ concentration was obtained by the difference of the two channels. Two scrubbing solutions were used for sampling the two species: a 1-mM phosphate buffer solution (pH 7) for the measurement of HONO and a 180 mM NH₄Cl/NH₃ buffer solution (pH 8.5) for the measurement of HONO+HNO₃. The scrubbing solution flow rate was 0.24 ml min⁻¹ and the gas sampling flow rate was 2 l min⁻¹. HNO₃ in the NH₄Cl/NH₃ buffer solution was quantitatively reduced to nitrite along an on-line 0.8-cm Cd reductor column. Nitrite in both channels was derivatized with 2 mM SA and 0.2 mM NED in 25 mM HCl. Quantitative derivatization was achieved within 5 min at 55°C. The azo dye derivative was then separated from the SA/NED reagent by reversed-phase HPLC and detected with a UV-vis detector at 540 nm. With an on-line SEP-PAK C-18 cartridge for the reagent purification, the method detection limit is estimated to be better than 1 pptv for HONO and about 20 pptv for HNO₃. The sample integration time was about 2 min and the sampling frequency is every 10 min. Data collected in downtown Albany and Whiteface Mountain, NY, are shown as examples of applications of this technique in both urban and remote clean environments.     

Secondary organic aerosol formation from the oxidation of aromatic hydrocarbons in the presence of dry submicron ammonium sulfate aerosol

A laboratory study was conducted to examine formation of secondary organic aerosols. A smog chamber system was developed for studying gas–aerosol interactions in a dynamic flow reactor. These experiments were conducted to investigate the fate of gas and aerosol phase compounds generated from hydrocarbon–nitrogen oxide (HC/NO_x) mixtures irradiated in the presence of fine (<2.5 μm) particulate matter. The goal was to determine to what extent photochemical oxidation products of aromatic hydrocarbons contribute to secondary organic aerosol formation through uptake on pre-existing inorganic aerosols in the absence of liquid water films. Irradiations were conducted with toluene, p-xylene, and 1,3,5-trimethylbenzene in the presence of NO_x and ammonium sulfate aerosol, with propylene added to enhance the production of radicals in the system. The secondary organic aerosol yields were determined by dividing the mass concentration of organic fraction of the aerosol collected on quartz filters by the mass concentration of the aromatic hydrocarbon removed by reaction. The mass concentration of the organic fraction was obtained by multiplying the measured organic carbon concentration by 2.0, a correction factor that takes into account the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. The mass concentrations of ammonium, nitrate, and sulfate concentrations as well as the total mass of the aerosols were measured. A reasonable mass balance was found for each of the aerosols. The largest secondary organic aerosol yield of 1.59±0.40% was found for toluene at an organic aerosol concentration of 8.2 μm⁻³, followed by 1.09±0.27% for p-xylene at 6.4 μg m⁻³, and 0.41±0.10% for 1,3,5-trimethylbenzene at 2.0 μg m⁻³. In general, these results agree with those reported by Odum et al. and appear to be consistent with the gas–aerosol partitioning theory developed by Pankow. The presence of organic in the aerosol did not affect significantly the hygroscopic properties of the aerosol.     

The continuous field measurements of soluble aerosol compositions at the Taipei Aerosol Supersite,Taiwan

The characteristics of ambient aerosols, affected by solar radiation, relative humidity, wind speed, wind direction, and gas–aerosol interaction, changed rapidly at different spatial and temporal scales. In Taipei Basin, dense traffic emissions and sufficient solar radiation for typical summer days favored the formation of secondary aerosols. In winter, the air quality in Taipei Basin was usually affected by the Asian continental outflows due to the long-range transport of pollutants carried by the winter monsoon. The conventional filter-based method needs a long time for collecting aerosols and analyzing compositions, which cannot provide high time-resolution data to investigate aerosol sources, atmospheric transformation processes, and health effects. In this work, the in situ ion chromatograph (IC) system was developed to provide 15-min time-resolution data of nine soluble inorganic species (Cl⁻, NO₂⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺). Over 89% of all particles larger than approximately 0.056 μm were collected by the in situ IC system. The in situ IC system is estimated to have a limit of detection lower than 0.3 μg m⁻³ for the various ambient ionic components. Depending on the hourly measurements, the pollutant events with high aerosol concentrations in Taipei Basin were associated with the local traffic emission in rush hour, the accumulation of pollutants in the stagnant atmosphere, the emission of industrial pollutants from the nearby factories, the photochemical secondary aerosol formation, and the long-range transport of pollutants from Asian outflows.     

Seasonal variations of acidic air pollutants in Seoul,South Korea

The annular denuder system (ADS) was used to characterize seasonal variations of acidic air pollutants in Seoul, South Korea. Fifty- four 24 h samples were collected over four seasons from October 1996 to September 1997. The annual mean concentrations of HNO₃, HNO₂, SO₂ and NH₃ in the gas phase were 1.09, 4.51, 17.3 and 4.34 μg m^-3, respectively. The annual mean concentrations of PM_2.5(d_p≤2.5 μm in aerodynamic diameter, 50% cutoff), SO^2-₄, NO^-₃ and NH⁺₄ in the particulate phase were 56.9, 8.70, 5.97 and 4.19 μg m^-3, respectively. All chemical species monitored from this study showed statistical seasonal variations. Nitric acid (HNO₃) and ammonia (NH₃) exhibited substantially higher concentrations during the summer, while nitrous acid (HNO₂) and sulfur dioxide(SO₂) were higher during the winter. Concentrations of PM_2.5, SO^2-₄, NO^-₃ and NH⁺₄ in the particulate phase were higher during the winter months. SO^2-₄, NO^-₃ and NH⁺₄ accounted for 26–38% of PM_2.5. High correlations were found among PM_2.5, SO^2-₄, NO^-₃ and NH⁺₄. The mean H⁺ concentration measured only in the fall was 5.19 nmole m^-3.     

Carbonaceous and inorganic composition in long-range transported aerosols over northern Japan: Implication for aging of water-soluble organic fraction

To better understand the influence of sources and atmospheric processing on aerosol chemical composition, we collected atmospheric particles in Sapporo, northern Japan during spring and early summer 2005 under the air mass transport conditions from Siberia, China and surrounding seas. The aerosols were analyzed for inorganic ions, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and the major water-soluble organic compound classes (i.e., dicarboxylic acids and sugars). SO₄^2? is the most abundant inorganic constituent (average 44% of the identified inorganic ion mass) followed by NH₄⁺ (21%) and NO₃^? (13%). Concentrations of OC, EC, and WSOC ranged from 2.0–16, 0.24–2.9, and 0.80–7.9 μg m^?3 with a mean of 7.4, 1.0, and 3.1 μg m^?3, respectively. High OC/EC ratios (range: 3.6–19, mean: 8.7) were obtained, however WSOC/OC ratios (0.23–0.69, 0.44) do not show any significant diurnal changes. These results suggest that the Sapporo aerosols were already aged, but were not seriously affected by local photochemical processes. Identified water-soluble organic compounds (diacids + sugars) account for <10% of WSOC. Based on some marker species and air mass back trajectory analyses, and using stable carbon isotopic compositions of shorter-chain diacids (i.e., C₂–C₄) as photochemical aging factor of organic aerosols, the present study suggests that a fraction of WSOC in OC is most likely influenced by aerosol aging, although the OC loading in aerosols may be more influenced by their sources and source regions.     

Deposition and adsorption of the air pollutant HNO3 vapor to soil surfaces

Deposition of nitric acid (HNO₃) vapor to soils has been evaluated in three experimental settings: (1) continuously stirred tank reactors with the pollutant added to clean air, (2) open-top chambers at high ambient levels of pollution with and without filtration reducing particulate nitrate levels, (3) two field sites with high or low pollution loads in the coastal sage plant community of southern California. The results from experiment (1) indicated that the amount of extractable NO₃⁻ from isolated sand, silt and clay fractions increased with atmospheric concentration and duration of exposure. After 32 days, the highest absorption of HNO₃ was determined for clay, followed by silt and sand. While the sand and silt fractions showed a tendency to saturate, the clay samples did not after 32 days of exposure under highly polluted conditions. Absorption of HNO₃ occurred mainly in the top 1 mm layer of the soil samples and the presence of water increased HNO₃ absorption by about 2-fold. Experiment (2) indicated that the presence of coarse particulate NO₃⁻ could effectively block absorption sites of soils for HNO₃ vapor. Experiment (3) showed that soil samples collected from open sites had about 2.5 more extractable NO₃⁻ as compared to samples collected from beneath shrub canopies. The difference in NO₃⁻ occurred only in the upper 1–2 cm as no significant differences in NO₃⁻ concentrations were found in the 2–5 cm soil layers. Extractable NO₃⁻ from surface soils collected from a low-pollution site ranged between 1 and 8 μg NO₃–N g⁻¹, compared to a maximum of 42 μg NO₃–N g⁻¹ for soils collected from a highly polluted site. Highly significant relationship between HNO₃ vapor doses and its accumulation in the upper layers of soils indicates that carefully prepared soil samples (especially clay fraction) may be useful as passive samplers for evaluation of ambient concentrations of HNO₃ vapor.     

Quantitative analysis of volatile organic compounds (VOCs) in atmospheric particles

There are a number of difficulties associated with the quantitative analysis of volatile organic compounds (VOCs) in atmospheric particles. Therefore, majority of the previous studies on VOCs associated with particles have been qualitative. Air samples were collected in Izmir, Turkey to determine ambient particle and gas phase concentrations of several aromatic, oxygenated and halogenated VOCs. Samples were quantitatively analyzed using thermal desorption–gas chromatography/mass spectrometry. Gas-phase concentrations ranged between 0.02 (bromoform) and 4.65 μg m⁻³ (toluene) and were similar to those previously measured at the same site. Particle-phase concentrations ranged from 1 (1,3-dichlorobenzene) to 933 pg m⁻³ (butanol). VOCs were mostly found in gas-phase (99.9±0.25%). However, the particulate VOCs had comparable concentrations to those reported previously for semivolatile organic compounds. The distribution of particle-phase VOCs between fine (d_p<2.5 μm) and coarse (2.5 μm<d_p<10 μm) fractions was also investigated. It was found that VOCs were mostly associated with fine particles.     

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.     

Nitric acid and the origin and size segregation of aerosol nitrate aloft during BRACE 2002

As part of the BRACE 2002 May field intensive, the NOAA Twin Otter flew 21 missions over terrestrial, marine, and mixed terrestrial and marine sites in the greater Tampa, Florida, airshed including over Tampa Bay and the Gulf of Mexico. Aerosols were collected with filter packs and their inorganic fractions analyzed post hoc with ion chromatography. Anion mass dominated both the fine- (particle diameters ⩽2.5 μm) and coarse-mode (particle diameters 10.0–2.5 μm) inorganic fractions: SO₄²⁻in the fine fraction, 3.7 μg m⁻³ on average and Cl⁻ and NO₃⁻ in the coarse fraction, 0.6 μg m⁻³ on average and 1.4 μg m⁻³ on average, respectively. Ammonium ion dominated the inorganic fine-mode cation mass, averaging 1.2 μg m⁻³, presumably in association with SO₄². Coarse-mode cation mass was dominated by Na⁺, but the concentrations of Ca²⁺ and K⁺ together often equaled or exceeded the Na⁺ mass which was, on average, 0.6 μg m⁻³. Nitrate appeared predominantly in the coarse rather than the fine fraction, as expected, and the fine fraction never contributed >15% of the total NO₃ concentration. Nitric acid dominated the NO₃⁻ contribution from both aerosol size fractions, and constituted at least 45% of the total NO₃ in all samples. Coarse-mode Cl⁻ depletion, and hence NO₃⁻ replacement, reached 100% within the first 4 h of plume travel from the urban core in some samples, although it was most often less than 100% and slightly below the expected 1:1 ratio with coarse-mode NO₃⁻ concentration: the slope of the regression line of NO₃⁻ concentration to Cl⁻ depletion was 0.9 in the coarse fraction. In addition, terrestrial samples were markedly lower in Cl⁻ depletion, and thus in substituted NO₃^–, than were marine and mixed samples: 15–25% depletion in terrestrial samples vs. 50–65% in marine samples with the same air mass age. Thus, we conclude that NO₃⁻ and its progenitor compound HNO₃ were present in the Tampa airshed in insufficient amounts to titrate fully the slightly alkaline coarse-mode particles there, and to replace completely the Cl⁻ from the coarse-mode NaCl.     

Characteristics of PM2.5 carbonaceous aerosol in the Sihwa industrial area,Korea

In order to investigate the characteristics of carbonaceous fine aerosols, PM_2.5 particulate samples were collected in the Sihwa industrial complex area between February 1998 and 1999 and in Seoul between 31 May and 9 June 1999, respectively. The carbonaceous species were analyzed by the selective thermal manganese dioxide oxidation (TMO) method. In Sihwa, average OC and EC concentrations for the entire data set were measured to be 9.8 and 1.8 μg m⁻³, respectively. The OC concentrations were higher than those measured in other urban environments. The EC concentrations were lower than those of other urban environments. The OC/EC ratio measured at the Sihwa area was higher than those at other urban and rural environments. Backward trajectories of sampled air masses were performed to find out the sources of those higher OC/EC levels. Enrichment in the organic compounds during winter periods can be explained by the combination of primary local emissions from the industrial complex area and long-range transport of organic species from outside the Sihwa area. High OC values in June resulted from primary anthropogenic emissions and secondary organic aerosol formation rather than the atmospheric transport of organic compounds from the outside. In urban area of Seoul, the OC and EC concentrations in PM_2.5 during the summer were higher than those measured at other urban atmospheres. OC/EC ratios obtained in Seoul were lower than Sihwa. It can be concluded that carbonaceous species in Seoul were mainly emitted from primary anthropogenic sources.     

Source apportionment of ambient PM2.5 at five spanish centres of the european community respiratory health survey (ECRHS II)

Fine particulate matter (PM_2.5) was sampled at 5 Spanish locations during the European Community Respiratory Health Survey II (ECRHS II). In an attempt to identify and quantify PM_2.5 sources, source contribution analysis by principal component analysis (PCA) was performed on five datasets containing elemental composition of PM_2.5 analysed by ED-XRF. A total of 4–5 factors were identified at each site, three of them being common to all sites (interpreted as traffic, mineral and secondary aerosols) whereas industrial sources were site-specific. Sea-salt was identified as independent source at all coastal locations except for Barcelona (where it was clustered with secondary aerosols). Despite their typically dominant coarse grain-size distribution, mineral and marine aerosols were clearly observed in PM_2.5. Multi-linear regression analysis (MLRA) was applied to the data, showing that traffic was the main source of PM_2.5 at the five sites (39–53% of PM_2.5, 5.1–12.0 μg m⁻³), while regional-scale secondary aerosols accounted for 14–34% of PM_2.5 (2.6–4.5 μg m⁻³), mineral matter for 13–31% (2.4–4.6 μg m⁻³) and sea-salt made up 3–7% of the PM_2.5 mass (0.4–1.3 μg m⁻³). Consequently, despite regional and climatic variability throughout Spain, the same four main PM_2.5 emission sources were identified at all the study sites and the differences between the relative contributions of each of these sources varied at most 20%. This would corroborate PM_2.5 as a useful parameter for health studies and environmental policy-making, owing to the fact that it is not as subject to the influence of micro-sitting as other parameters such as PM₁₀. African dust inputs were observed in the mineral source, adding on average 4–11 μg m⁻³ to the PM_2.5 daily mean during dust outbreaks. On average, levels of Al, Si, Ti and Fe during African episodes were higher by a factor of 2–8 with respect to non-African days, whereas levels of local pollutants (absorption coefficient, S, Pb, Cl) showed smaller variations (factor of 0.5–2).     

Sources and concentrations of gaseous and particulate reduced nitrogen in the city of Münster (Germany)

Atmospheric ammonia mixing ratios and the main inorganic ions NH₄⁺, NO₃⁻ and SO₄²⁻ of size-resolved particles in the range from 0.05 to 10 μm were measured at an urban site in Münster, Germany. High mixing ratios of ammonia with a median of 5.2 ppb and a maximum of 50 ppb were detected. The mass fraction of submicron particles was much higher during the day than at night. At night, a greater particle mass and an increased presence of particulate nitrate was measured. Recurring patterns of particle distribution were distinguished and their characteristics analysed. In half of the measurements, the accumulation mode was clearly dominating, which is an indication of aged aerosol. In some measurements, higher concentrations of fine particles were found indicating particle formation. In these cases, a smaller particle mass and about four times greater ratios of ammonia versus ammonium concentrations were observed. These data show that ammonia contributes considerably to the formation of secondary particulate material.     

Changes in soil inorganic nitrogen as related to atmospheric nitrogenous pollutants in southern California

The deposition of nitrogenous pollutants has serious implications for ecosystem function and stability. Research in temperate ecosystems has indicated a wide range of ecological responses, yet very little is known about arid ecosystems. In this study, measurements of atmospheric and soil concentrations of the plant-available NO^-₃ and NH⁺₄ were evaluated to identify a potential gradient in nitrogen (N) deposition. The evaluations were conducted in coastal sage scrub, a semi-arid vegetation type native to the lower elevations of southern California.The summer atmospheric concentrations of nitrate (NO^-₃) and ammonium (NH⁺₄) were determined at five locations on the Perris Plain of southern California. The atmospheric influences varied from direct interception of pollution generated in the Los Angeles Basin at the northern end of the gradient to a site 70 km south lacking any direct Los Angeles influence. The summer atmospheric concentrations of NO^-₃ varied more than three-fold along the gradient. Ammonium concentrations followed a similar pattern, but the gradient was less steep. Winter concentrations were very low for both compounds. The summer soil surface NO^-₃ concentrations were near the detection limits at low pollution sites but in the range of 50–60 μg N g^-1 soil under highly polluted conditions. Wet deposition was found to be a minor contributor of plant-available N, suggesting that dry deposition may be a consequential source of plant-available N.The detection of significant changes in inorganic, plant-available N in the upper layer of soils is enhanced by the unique environmental conditions and vegetation of southern California. This study suggests that the coastal sage scrub ecosystem is experiencing significant changes in N fertility that may contribute to changes in plant species composition. The data also show that this semi-arid ecosystem provides a unique opportunity to assess many physical, chemical and biological responses to dry deposition alone.     

Modelling long-range transport of primary particulate material over Europe

This paper uses a simple model of atmospheric transport and an emissions inventory prepared by TNO to estimate the contribution of primary particulate material to PM₁₀ and PM_2.5 concentration across Europe. The resulting population exposure is compared with that of secondary particulates, and it is noted that both primary and secondary contributions will be significantly reduced with the implementation of new protocols under the Convention on Long-Range Transboundary Air Pollution (CLRTAP). Since concentrations of primary PM₁₀ can become elevated in episodic situations, when long-range transport of particulate could, on its own, exceed 24 h average targets of 50 μg m⁻³ over large areas of Europe, such reduction is important for achievement of current air quality standards to control exposure to atmospheric particulate PM₁₀.     

Study of size distribution of atmospheric aerosol at Agra

Measurements on size distribution of atmospheric aerosol were made at Dayalbagh, Agra during July to September 1998. A 4-stage cascade particle sampler (CPS - 105) which fractionates particles in sizes ranging between 0.7 and >10.9 μm, was used. Samples were collected on Whatman 41 filters. The filters were analyzed for the major water-soluble ions. The anions (F, Cl, NO₃ and SO₄) were analyzed by Dionex DX-500 ion chromatograph while atomic absorption and colorimetric techniques were used for the analysis of cations (Na, K, Ca and Mg) and NH₄, respectively. The average mass of aerosol was found to be 131.6 μg m⁻³ and aerosol composition was found to be influenced by terrigeneous sources. The mass size distribution of total aerosol and the ions NH₄, Cl, NO₃, K, Ca, Mg, SO₄ and Na was bimodal while that of F was unimodal. SO₄, F, K and NH₄ dominated in the fine mode while Ca, Mg, Cl and NO₃ were in abundance in coarse fraction. Na was found in both coarse as well as fine mode. Coarse mode SO₄ and NO₃ have been ascribed to contribution from re-suspension of soil and formation by heterogeneous oxidation on soil derived particles. Preponderance of K in fine mode is attributed to emissions from vegetation and from burning of plant materials. Ca, Mg, Cl and NO₃ are largely soil derived and hence dominate in coarse fraction. Equivalent ratios of NH₄/(SO₄+NO₃) were calculated for both fine and coarse aerosols. The coarse mode ratio varied between 0.7 and 1.4 while in fine mode it ranged between 1.4 and 1.9. It shows that aerosol is basic, the basicity of coarse mode is due to higher concentration of soil-derived alkaline components while the basicity in fine mode is due to neutralization of acidity by NH₃.     

Physical characterization of aerosol particles during the Chinese New Year’s firework events

Measurements for particles 10 nm to 10 μm were taken using a Wide-range Particle Spectrometer during the Chinese New Year (CNY) celebrations in 2009 in Shanghai, China. These celebrations provided an opportunity to study the number concentration and size distribution of particles in an especial atmospheric pollution situation due to firework displays. The firework activities had a clear contribution to the number concentration of small accumulation mode particles (100–500 nm) and PM₁ mass concentration, with a maximum total number concentration of 3.8 × 10⁴ cm^?3. A clear shift of particles from nucleation and Aitken mode to small accumulation mode was observed at the peak of the CNY firework event, which can be explained by reduced atmospheric lifetimes of smaller particles via the concept of the coagulation sink. High particle density (2.7 g cm^?3) was identified as being particularly characteristic of the firework aerosols. Recalculated fine particles PM₁ exhibited on average above 150 μg m^?3 for more than 12 hours, which was a health risk to susceptible individuals. Integral physical parameters of firework aerosols were calculated for understanding their physical properties and further model simulation.