Use of passive samplers to measure atmospheric ammonia levels in a high-density industrial hog farm area of eastern North Carolina

Hog concentrated animal feeding operations (CAFOs) in North Carolina release ammonia (NH₃), hydrogen sulfide, VOCs, and particulate matter to the atmosphere. These operations are located mainly in the NC coastal plain and can create potential health hazards for nearby human populations. Limited work has been performed to measure NH₃ at the community level to assess potential human exposure. In an effort to address this issue, a study was designed to measure NH₃ levels near hog CAFOs and community locations (i.e. homes and schools) in Eastern NC.NH₃ was collected using passive diffusion tubes in triplicate exposed primarily in weekly intervals. Sampling occurred from October 2003 to May 2004 (20 sites) and from July 2004 to October 2004 (23 sites) at varying distances from hog CAFOs in close proximity to homes and schools. Average weekly NH3 levels were measured as mass (μg NH₃-N) and converted to concentration (ppb). Mean level of 13.8 ppb near homes and schools (<2 km) was 4–12 times greater than ambient background levels (1–3 ppb), reaching as high as 80 ppb. Exposed sites (<2 km from a hog CAFO) had a mean level of 12.8 ppb which was over 2 times higher than the mean level of 5.5 ppb at less exposed sites (>2 km from a hog CAFO).The study establishes that passive sampling can be effectively used to measure average atmospheric ammonia levels at community locations near hog CAFOs in Eastern NC. The collected data indicate the relative exposure for human populations who live near a hog CAFO. The closer a populace is to the hog CAFO, the more intense the exposure. These results require more validation in the field by comparison to a reference method.     

Ambient sulfur dioxide,nitrogen dioxide,and ammonia at ten background and rural sites in China during 2007–2008

We present two years (January 2007–December 2008) of atmospheric SO₂, NO₂ and NH₃ measurements from ten background or rural sites in nine provinces in China. The measurements were made on a monthly basis using passive samplers under careful quality control. The results show large geographical and seasonal variations in the concentrations of these gases. The mean SO₂ concentration varied from 0.7 ± 0.4 ppb at Waliguan on Qinghai Plateau to 67.3 ± 31.1 ppb at Kaili in Guizhou province. The mean NO₂ concentration ranged from 0.6 ± 0.4 ppb at Waliguan to 23.9 ± 6.9 ppb at Houma in southern Shanxi. The mean NH₃ concentration ranged from 2.8 ± 3.0 ppb at Shangdianzi in northeastern Beijing to 13.7 ± 8.4 ppb at Houma. At most sites, SO₂ and NO₂ peaked in winter and reached minima in summer, while NH₃ showed maximum values in summer and lower values in cold seasons. On the whole, the geographical distributions of the observed gas concentrations are consistent with those of emissions. The ground measurements of SO₂ and NO₂ are contrasted to the SCIAMACHY SO₂ and OMI NO₂ tropospheric columns, respectively. Although the satellite data can capture the main features of emissions and concentrations of SO₂, they do not reflect the variations of SO₂ in the surface layer. The situation is better for the case of NO₂. The OMI NO₂ columns capture the geographical differences in the ground NO₂ and correlate fairly well with the ground levels of NO₂ at six of the ten sites.     

Surface ozone and NOx concentrations at a high altitude Mediterranean site,Greece

Ozone was measured in six- and NO_x in five sampling periods in 1996–97, mostly during summer, at a 1070 m altitude site in northern Peloponnese. Mean values in each sampling period ranged from 43–48 ppb exceeding the European Union 24 h plant protection standard. The background ozone concentration of 43 ppb derived from the correlation of ozone with NO^′_x also exceeded the EU plant protection standard. Ozone exhibited maxima in the afternoon and minima during the night; in certain 24–48 h periods, however, the ozone concentrations remained practically constant; in these short periods air mass back trajectories indicated air masses which originated in north Africa. NO^′_x concentrations had maximum of 24 h around noon. Their mean concentrations ranged from 0.5–0.7 ppb, smaller than respective concentrations in north-central Europe.     

Measurement and analysis of atmospheric ammonia emissions from anaerobic lagoons

Ammonia-nitrogen flux (NH₃-N=(14/17)NH₃) was determined from six anaerobic swine waste storage and treatment lagoons (primary, secondary, and tertiary) using the dynamic chamber system. Measurements occurred during the fall of 1998 through the early spring of 1999, and each lagoon was examined for approximately one week. Analysis of flux variation was made with respect to lagoon surface water temperature (∼15 cm below the surface), lagoon water pH, total aqueous phase NH_x(=NH₃+NH₄⁺) concentration, and total Kjeldahl nitrogen (TKN). Average lagoon temperatures (across all six lagoons) ranged from approximately 10.3 to 23.3^°C. The pH ranged in value from 6.8 to 8.1. Aqueous NH_x concentration ranged from 37 to 909 mg N l⁻¹, and TKN varied from 87 to 950 mg N l⁻¹. Fluxes were the largest at the primary lagoon in Kenansville, NC (March 1999) with an average value of 120.3 μg N m⁻² min⁻¹, and smallest at the tertiary lagoon in Rocky Mount, NC (November 1998) at 40.7 μg N m⁻² min⁻¹. Emission rates were found to be correlated with both surface lagoon water temperature and aqueous NH_x concentration. The NH₃-N flux may be modeled as ln(NH₃-N flux)=1.0788+0.0406T_L+0.0015([NH_x]) (R²=0.74), where NH₃-N flux is the ammonia flux from the lagoon surface in μg N m⁻² min⁻¹, T_L is the lagoon surface water temperature in ^°C, and [NH_x] is the total ammonia-nitrogen concentration in mg N l⁻¹.     

Dry deposition of ammonia,nitric acid,ammonium, and nitrate to alpine tundra at Niwot Ridge,Colorado

Micrometeorological measurements and ambient air samples, analyzed for concentrations of NH₃, HNO₃, NH₄⁺, and NO₃⁻, were collected at an alpine tundra site on Niwot Ridge, Colorado. The measured concentrations were extremely low and ranged between 5 and 70 ng N m⁻³. Dry deposition fluxes of these atmospheric species were calculated using the micrometeorological gradient method. The calculated mean flux for NH₃ indicates a net deposition to the surface and indicates that NH₃ contributed significantly to the total N deposition to the tundra during the August–September measurement period. Our pre-measurement estimate of the compensation point for NH₃ in air above the tundra was 100–200 ng N m⁻³; thus, a net emission of NH₃ was expected given the low ambient concentrations of NH₃ observed. Based on our results, however, the NH₃ compensation point at this alpine tundra site appears to have been at or below about 20 ng N m⁻³. Large deposition velocities (>2 cm s⁻¹) were determined for nitrate and ammonium and may result from reactions with surface-derived aerosols.     

Ozone assessment in the southern part of the Alps

In this paper ozone measurements carried out at six alpine and prealpine sites, located in the Italian region of Central Alps are shown. The stations are placed at altitudes between 800 and 1900 m a.s.l., far away from local sources of pollution. Ozone concentrations appear to be quite uniform, with summer mean values varying from 40 to 47 ppb and winter ones from 19 to 35 ppb. The number of hours exceeding the 75 and 100 ppb WHO thresholds and the AOT40 (Average Over Threshold 40 ppb of ozone) are evaluated for the growing season. The temporal variability of weekly ozone cycle at alpine stations provides useful informations to assess an emission control strategy.     

Measurement of the vertical profile of atmospheric SO2 during the heating period in Beijing on days of high air pollution

This paper reports altitude-resolved concentrations of sulfur dioxide (SO₂) and particulate matter up to 10 microns in diameter (PM₁₀) in the planetary boundary layer of major urban centers during extreme pollution episodes. The concentration of SO₂ was observed continuously from November 24, 2004, to December 4, 2004, in Beijing during the heating period. Fluorescence SO₂ analyzers were used to measure the atmospheric SO₂ concentrations. Four SO₂ analyzers were placed at 4 different levels (8 m, 47 m, 120 m, and 280 m) of the 325-m high meteorological observation tower of the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences. A maximal SO₂ concentration of 172.3 ppb was measured during this pollution episode, and SO₂ concentration increased with altitude and reached its maximal value at ～50 m. The study also analyzed the meteorological situation before, during, and after the pollution episode.     

Trace gas variations at Cape Point,South Africa,during May 1997 following a regional biomass burning episode

During the continuous monitoring of atmospheric parameters at the station Cape Point (34°S, 18°E), a smoke plume originating from a controlled fire of 30-yr-old fynbos was observed on 6 May 1997. For this episode, which was associated with a nocturnal inversion and offshore airflow, atmospheric parameters (solar radiation and meteorological data) were considered and the levels of various trace gases compared with those measured at Cape Point in maritime air. Concentration maxima in the morning of 6 May for CO₂, CO, CH₄ and O₃ amounted to 370.3 ppm, 491 ppb, 1730 ppb and 47 ppb, respectively, whilst the mixing ratios of several halocarbons (F-11, F-12, F-113, CCl₄ and CH₃CCl₃) remained at background levels. In the case of CO, the maritime background level for this period was exceeded by a factor of 9.8. Differences in ozone levels of up to 5 ppb between air intakes at 4 and 30 m above the station (located at 230 m above sea level) indicated stratification of the air advected to Cape Point during the plume event. Aerosols within the smoke plume caused the signal of global solar radiation and UV–A to be attenuated from 52.4 to 13.0 mW cm⁻² and from 2.3 to 1.3 mW cm⁻², respectively, 5 h after the trace gases had reached their maxima. Emission ratios (ERs) calculated for CO and CH₄ relative to CO₂ mixing ratios amounted to 0.042 and 0.0040, respectively, representing one of the first results for fires involving fynbos. The CO ER is somewhat lower than those given in the literature for African savanna fires (average ER=0.048), whilst for CH₄ the ER falls within the range of ERs reported for the flaming (0.0030) and smouldering phases (0.0055) of savanna fires. Non-methane hydrocarbon (NMHC) data obtained from a grab sample collected during the plume event were compared to background levels. The highest ERs (ΔNMHC/ΔCH₄) have been obtained for the C₂–C₃ hydrocarbons (e.g. ethene at 229.3 ppt ppb⁻¹), whilst the C₄–C₇ hydrocarbons were characterised by the lowest ERs (e.g. n-hexane at 1.0 and n-pentane at 0.8 ppt ppb⁻¹).     

Ammonia fluxes and derived canopy compensation points over non-fertilized agricultural grassland in The Netherlands using the new gradient ammonia—high accuracy—monitor (GRAHAM)

During a measurement period from June till November 2004, ammonia fluxes above non-fertilized managed grassland in The Netherlands were measured with a Gradient Ammonia—High Accuracy—Monitor (GRAHAM). Compared with earlier ammonia measurement systems, the GRAHAM has higher accuracy and a quality control system.Flux measurements are presented for two different periods, i.e. a warm, dry summer period (from 18 July till 15 August) and a wet, cool autumn period (23 September till 23 October). From these measurements canopy compensation points were derived. The canopy compensation point is defined as the effective surface concentration of ammonia. In the summer period (negative) deposition fluxes are observed in the evening, night and early morning due to leaf surface wetness, while in the afternoon emission fluxes are observed due to high canopy compensation points. The mean NH₃-flux in this period was 4 ng m⁻² s⁻¹, which corresponds to a net emission of 0.10 kg N ha⁻¹ over the 28 day sampling period. The NH₃-flux in the autumn period mainly shows (negative) deposition fluxes due to small canopy compensation points caused by low temperatures and a generally wet surface. The mean NH₃-flux in this period is −24 ng m⁻² s⁻¹, which corresponds to a net deposition of 0.65 kg N ha⁻¹ over the 31 day sampling period.Frequency distributions of the NH₃-concentration and flux show that despite higher average ambient NH₃-concentrations (13.3 μg m⁻³ in the summer period vs. 6.4 μg m⁻³ in the autumn period) there are more emission events in the summer period than in the autumn period (about 50% of the time in summer vs. 20% in autumn). This is caused by the high canopy compensation points in summer due to high temperatures and a dry surface. In autumn, deposition dominates due to a generally wet surface that induces low canopy compensation points.For our non-fertilized agricultural grassland site, the derived canopy compensation points (at temperatures between 7 and 29 °C) varied from 0.5 to 29.7 μg m⁻³ and were on an average 7.0 μg m⁻³, which is quite high for non-fertilized conditions and probably caused by high nitrogen inputs in the past or high dry deposition amounts from local sources. The average value for the ratio between NH₄⁺ and H⁺ concentration in the canopy, Γ_c, that was derived from our data was 2200.     

Tropical tropospheric ozone observed in Thailand

The mixing ratios of surface ozone at two rural/remote sites in Thailand, Inthanon and Srinakarin, have been measured continuously for the first time. Almost identical seasonal variations of O₃ with dry season maximum and a wet season minimum with a large seasonal amplitude are observed at both sites during 1996–1998. At Inthanon, the monthly averaged O₃ mixing ratios range 9–55 ppb, with the annual average of 27 ppb. The ozone mixing ratios at Srinakarin are in the similar range, 9–45 ppb with annual average of 28 ppb. Based on trajectory analysis of O₃ data at Inthanon, the long-range transport of O₃ under Asian monsoon regime could primarily explain the low O₃ mixing ratios of 13 ppb in clean marine air mass from Indian Ocean during wet season but only partly explain the relatively low O₃ mixing ratios, 26 ppb or less, in continental air mass from northeast Asia either in wet or dry season. The highest O₃ mixing ratios are found in air masses transported within southeast Asia, averaged 46 ppb in dry season. The high O₃ mixing ratios during the dry season are suggested to be significantly due to the local/sub-regional scale O₃ production triggered by biomass burning in southeast Asia rather than long-range transport effect.     

Biases in Clean Air Status and Trends Network filter pack results associated with sampling protocol

Network filter pack sampling protocol changed in 1989 from requiring a week-long daytime sample and a week-long nighttime sample to requiring a single week-long sample per week at each monitoring site. In the current study, single-filter pack weekly results are compared with weekly results aggregated from separate daytime and nighttime weekly filter pack samples collected at the monitoring site located at Egbert, Ontario, Canada. Comparisons of the concentrations resulting from the two sampling protocols for all major chemical species (SO₄²⁻, NO₃⁻, NH₄⁺, HNO₃, and SO₂) show median biases of <5 nmol m⁻³ (0.1 ppb) and median relative biases of <10%. Median relative biases have the same sign for each species, suggesting biases in the same direction. Based on median differences, composite day–night weekly sampler results generally exceed the single-sampler weekly results (in all cases except for the summer nylon filter HNO₃), and the magnitude depends on the constituent and on the season. Examination of seasonal results reveals large discrepancies in some cases, especially during summer. To use Clean Air Status and Trends Network results for trends analyses over time periods encompassing the 1989 protocol change, it may be useful to put all of the data on the same basis of sampler protocol. Algorithms derived from linear regression analyses using paired bootstrap sampling are offered to convert the recent results to the pre-1989 basis; however, they may only be appropriate for sites in the eastern US. Chemical and statistical reasoning suggests that the results of day–night weekly sampling are usually consistent with higher accuracy than single-sampler weekly results. Adjustments are indicated for summer Teflon NO₃ and nylon HNO₃, for summer and fall Teflon NH₄, and for Total SO₂ in each season. Nylon filters are also shown to have variable collection characteristics for SO₂ that are consistent with a humidity effect. A network-wide change in the SO₂ collection and/or retention characteristics of the nylon filters is found in April 1997.     

Sulfuric odorous compounds emitted from pig-feeding operations

The objective of the study was to quantify the concentration and emission levels of sulfuric odorous compounds emitted from pig-feeding operations. Five types of pig-housing rooms were studied: gestation, farrowing, nursery, growing and fattening rooms. The concentration range of sulfuric odorous compounds in these pig-housing rooms were 30–200 ppb for hydrogen sulfide (H₂S), 2.5–20 ppb for methyl mercaptan (CH₃SH), 1.5–12 ppb for dimethyl sulfide (DMS; CH₃SCH₃) and 0.5–7 ppb for dimethyl disulfide (DMDS; CH₃S₂CH₃), respectively. The emission rates of H₂S, CH₃SH, DMS and DMDS were estimated by multiplying the average concentration (mg m⁻³) measured near the air outlet by the mean ventilation rate (m³ h⁻¹) and expressed either per area (mg m⁻² h⁻¹) or animal unit (AU; liveweight of the pig, 500 kg) (mg pig⁻¹ h⁻¹). As a result, the emission rates of H₂S, CH₃SH, DMS and DMDS in the pig-housing rooms were 14–64, 0.8–7.3, 0.4–3.4 and 0.2–1.9 mg m⁻² h⁻¹, respectively, based on pig's activity space and 310–723, 18–80, 9–39 and 5–22 mg AU⁻¹ h⁻¹, respectively, based on pig's liveweight, which indicates that their emission rates were similar, whether based upon the pig's activity space or liveweight. In conclusion, the concentrations and emission rates of H₂S were highest in the fattening room followed by the growing, nursery, farrowing and gestation rooms whereas those of CH₃SH, DMS and DMDS concentrations were largest in the growing room followed by the nursery, gestation and farrowing rooms.     

Benzene,toluene, ozone,NO2 and SO2 measurements in an urban street canyon in Thessaloniki,Greece

Benzene, toluene, sulphur dioxide, ozone and nitrogen dioxide were measured at a mean level of 13.5 m above ground in a narrow, four-lane street canyon (height 30 m, width 20 m) in Thessaloniki, Greece during the period January–July 1997 by means of a commercial differential optical absorption spectrometer (OPSIS DOAS). Primary pollutant levels were found to be 2.5–4.4 times higher during the cold part of the year than during the warm part of the year, the winter/summer ratio increasing with the reaction rate constant with OH for each of the measured species. Ozone, on the other hand, exhibited a winter/summer ratio of 0.36. NO₂ originates from both primary and secondary sources; its winter/summer concentration ratio of 1.4 lies, therefore, between those of primary pollutants and ozone. Pollution levels were influenced considerably by wind speed, while for the street canyon under study wind direction did not influence pollutant levels considerably. While primary pollution was found to decrease with increasing wind speed, ozone increased. Benzene mean levels during the study period were around 6 ppb and hence much higher than the EU annual limit value of 5 μg m⁻³ (1.44 ppb at STP). Toluene mean levels were around 14 ppb and hence also several times above the WHO recommendation of 2 ppb for 24 h. The apportionment of traffic emissions in four time zones used in most inventories in urban airshed models was tested using benzene and toluene measurements at low (<1 m s⁻¹) wind speeds. The agreement between model emissions and calculated emissions apportionment into the four time zones was good, except for Zone D (23:00–1:59), where model inventory emissions were somewhat too low.     

Air concentrations and wet deposition of major inorganic ions at five non-urban sites in China, 2001–2003

Air and precipitation measurements at five sites were undertaken from 2001 to 2003 in four different provinces in China, as part of the acid rain monitoring program IMPACTS. The sites were located in Tie Shan Ping (TSP) in Chongqing, Cai Jia Tang (CJT) in Hunan, Lei Gong Shan (LGS) and Liu Chong Guan (LCG) in Guizhou and Li Xi He (LXH) in Guangdong. The site characteristics are quite varied with TSP and LCG located relatively near big cites while the three others are situated in more regionally representative areas. The distances to urban centres are reflected in the air pollution concentrations, with annual average concentrations of SO₂ ranging from 0.5 to above 40 μg S m⁻³. The main components in the airborne particles are (NH₄)₂SO₄ and CaSO₄. Reduced nitrogen has a considerably higher concentration level than oxidised nitrogen, reflecting the high ammonia emissions from agriculture. The gas/particle ratio for the nitrogen compounds is about 1:1 at all the three intensive measurement sites, while for sulphur it varies from 2.5 to 0.5 depending on the distance to the emission sources. As in air, the predominant ions in precipitation are sulphate, calcium and ammonium. The volume weighted annual concentration of sulphate ranges from about 70 μeq l⁻¹ at the most rural site (LGS) to about 200 μeq l⁻¹ at TSP and LCG. The calcium concentration ranges from 25 to 250 μeq l⁻¹, while the total nitrogen concentration is between 30 and 150 μeq l⁻¹; ammonium is generally twice as high as nitrate. China's acid rain research has traditionally been focused on urban sites, but these measurements show a significant influence of long range transported air pollutants to rural areas in China. The concentration levels are significantly higher than seen in most other parts of the world.     

Ammonia volatilization from sows on grassland

According to regulations, sows with piglets on organic farms must graze on pastures. Volatilization of ammonia (NH₃) from urine patches may represent a significant source of nitrogen (N) loss from these farms. Inputs of N are low on organic farms and losses may reduce crop production. This study examined spatial variations in NH₃ volatilization using a movable dynamic chamber, and the pH and total ammoniacal nitrogen (TAN) content in the topsoil of pastures with grazing sows was measured during five periods between June 1998 and May 1999. Gross NH₃ volatilization from the pastures was also measured with an atmospheric mass balance technique during seven periods from September 1997 until June 1999. The dynamic chamber study showed a high variation in NH₃ volatilization because of the distribution of urine; losses were between 0 and 2.8 g NH₃–N m⁻² day⁻¹. Volatilization was highest near the feeding area and the huts, where the sows tended to urinate. Ammonia volatilization rate was linearly related to the product of NH₃ concentration in the boundary layer and wind speed. The NH₃ in the boundary layer was in equilibrium with NH₃ in soil solution. Gross NH₃ volatilization was in the range 0.07–2.1 kg NH₃–N ha⁻¹ day⁻¹ from a pasture with 24 sows ha⁻¹. Ammonia volatilization was related to the amount of feed given to the sows, incident solar radiation and air temperature during measuring periods, and also to temperature, incident solar radiation and rain 1–2 days before measurements. Annual ammonia loss was 4.8 kg NH₃–N sow⁻¹.     

Concentration-dependent NH3 deposition processes for moorland plant species with and without stomata

Currently, in operational modelling of NH₃ deposition a fixed value of canopy resistance (R_c) is generally applied, irrespective of the plant species and NH₃ concentration. This study determined the effect of NH₃ concentration on deposition processes to individual moorland species. An innovative flux chamber system was used to provide accurate continuous measurements of NH₃ deposition to Deschampsia cespitosa (L.) Beauv., Calluna vulgaris (L.) Hull, Eriophorum vaginatum L., Cladonia spp., Sphagnum spp., and Pleurozium schreberi (Brid.) Mitt. Measurements were conducted across a wide range of NH₃ concentrations (1–140 μg m⁻³).NH₃ concentration directly affects the deposition processes to the vegetation canopy, with R_c, and cuticular resistance (R_w) increasing with increasing NH₃ concentration, for all the species and vegetation communities tested. For example, the R_c for C. vulgaris increased from 14 s m⁻¹ at 2 μg m⁻³ to 112 s m⁻¹ at 80 μg m⁻³. Diurnal variations in NH₃ uptake were observed for higher plants, due to stomatal uptake; however, no diurnal variations were shown for non-stomatal plants. R_c for C. vulgaris at 80 μg m⁻³ was 66 and 112 s m⁻¹ during day and night, respectively. Differences were found in NH₃ deposition between plant species and vegetation communities: Sphagnum had the lowest R_c (3 s m⁻¹ at 2 μg m⁻³ to 23 at 80 μg m⁻³), and D. cespitosa had the highest nighttime value (18 s m⁻¹ at 2 μg m⁻³ to 197 s m⁻¹ at 80 μg m⁻³).     

Concentration-dependent NH3 deposition processes for mixed moorland semi-natural vegetation

Dry deposition modelling typically assumes that canopy resistance (R_c) is independent of ammonia (NH₃) concentration. An innovative flux chamber system was used to provide accurate continuous measurements of NH₃ deposition to a moorland composed of a mixture of Calluna vulgaris (L.) Hull, Eriophorum vaginatum L. and Sphagnum spp. Ammonia was applied at a wide range of concentrations (1–100 μg m⁻³). The physical and environmental properties and the testing of the chamber are described, as well as results for the moorland vegetation using the ‘canopy resistance’ and ‘canopy compensation point’ interpretations of the data.Results for moorland plant species demonstrate that NH₃ concentration directly affects the rate of NH₃ deposition to the vegetation canopy, with R_c and cuticular resistance (R_w) increasing with increasing NH₃ concentrations. Differences in R_c were found between night and day: during the night R_c increases from 17 s m⁻¹ at 10 μg m⁻³ to 95 s m⁻¹ at 80 μg m⁻³, whereas during the day R_c increases from 17 s m⁻¹ at 10 μg m⁻³ to 48 s m⁻¹ at 80 μg m⁻³. The lower resistance during the day is caused by the stomata being open and available as a deposition route to the plant. R_w increased with increasing NH₃ concentrations and was not significantly different between day and night (at 80 μg m⁻³ NH₃ day R_w=88 s m⁻¹ and night R_w=95 s m⁻¹). The results demonstrate that assessments using fixed R_c will over-estimate NH₃ deposition at high concentrations (over ∼15 μg m⁻³).     

Gaseous emission during the composting of pig feces from Chinese Ganqinfen system

The Ganqinfen system – a process of manually cleaning animal feces by means of a shovel – is a widely used manure separating method in Chinese pig farms. Ganqinfen pig feces and chopped corn stalks were mixed at the ratio of 7:1, and composted in 1.5 m³ rotting boxes for 70 d. Evolution of CH₄, N₂O and NH₃ during composting, and the effects of turning and covering, were studied in this research. Results showed that 20–39% and 0.5–4% of total nitrogen were lost in the form of NH₃ and N₂O respectively, and 0.1–0.9% of initial organic carbon was emitted as CH₄. Turning enhanced air exchange in the piles, thus decreasing CH₄ emission by 83–93% and shortening the maturing period. When trials were finished, all non-turned piles were separated to three layers by moisture content. This structure caused the N₂O losses of non-turning treatments to be 6–12.7 times higher than that of turning treatments. Covering materials reduced air exchange at the surface of the pile, thus decreasing the O₂ supply and consequently increasing CH₄ production by 33–45%. Covering also reduced NH₃ emission by 4–34%. For the composting of Ganqinfen pig feces, we suggest that a program of turning twice weekly without covering will result in compost that is sufficiently matured after 6 wk with the lowest resultant greenhouse gas emission.     

Surface ozone background in the United States: Canadian and Mexican pollution influences

We use a global chemical transport model (GEOS-Chem) with 1° × 1° horizontal resolution to quantify the effects of anthropogenic emissions from Canada, Mexico, and outside North America on daily maximum 8-hour average ozone concentrations in US surface air. Simulations for summer 2001 indicate mean North American and US background concentrations of 26 ± 8 ppb and 30 ± 8 ppb, as obtained by eliminating anthropogenic emissions in North America vs. in the US only. The US background never exceeds 60 ppb in the model. The Canadian and Mexican pollution enhancement averages 3 ± 4 ppb in the US in summer but can be occasionally much higher in downwind regions of the northeast and southwest, peaking at 33 ppb in upstate New York (on a day with 75 ppb total ozone) and 18 ppb in southern California (on a day with 68 ppb total ozone). The model is successful in reproducing the observed variability of ozone in these regions, including the occurrence and magnitude of high-ozone episodes influenced by transboundary pollution. We find that exceedances of the 75 ppb US air quality standard in eastern Michigan, western New York, New Jersey, and southern California are often associated with Canadian and Mexican pollution enhancements in excess of 10 ppb. Sensitivity simulations with 2020 emission projections suggest that Canadian pollution influence in the Northeast US will become comparable in magnitude to that from domestic power plants.     

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.