Ammonia emissions from non-agricultural sources in the UK

Atmospheric Environment 34 (2000) 855}869

Ammonia emissions from non-agricultural sources in the UK M.A. Sutton*, U. Dragosits, Y.S. Tang, D. Fowler Institute of Terrestrial Ecology, Edinburgh Research Station, Bush Estate, Penicuik, Midlothian EH26 0QB, Scotland, UK Received 12 January 1999; received in revised form 21 July 1999; accepted 5 August 1999

Abstract A detailed literature review has been undertaken of the magnitude of non-agricultural sources of ammonia (NH ) in 3 the United Kingdom. Key elements of the work included estimation of nitrogen (N) excreted by di!erent sources (birds, animals, babies, human sweat), review of miscellaneous combustion sources, as well as identi"cation of industrial sources and use of NH as a solvent. Overall the total non-agricultural emission of NH from the UK in 1996 is estimated here as 3 3 54 (27}106) kt NH }N yr~1, although this includes 11 (6}23) kt yr~1 from agriculture related sources (sewage sludge 3 spreading, biomass burning and agro-industry). Compared with previous estimates for 1990, component source magnitudes have changed both because of revised average emissions per source unit (emission factors) and changes in the source activity between 1990 and 1996. Sources with larger average emission factors than before include horses, wild animals and sea bird colonies, industry, sugar beet processing, household products and non-agricultural fertilizer use, with the last three sources being included for the "rst time. Sources with smaller emission factors than before include: land spreading of sewage sludge, direct human emissions (sweat, breath, smoking, infants), pets (cats and dogs) and fertilizer manufacture. Between 1990 and 1996 source activities increased for sewage spreading (due to reduced dumping at sea) and transport (due to increased use of catalytic converters), but decreased for coal combustion. Combined with the current UK estimates of agricultural NH emissions of 229 kt N yr ~1 (1996), total UK NH emissions are estimated at 3 3 283 kt N yr ~1. Allowing for an import of reduced nitrogen (NH ) of 30 kt N yr~1 and deposition of 230 kt N yr~1, these x "gures imply an export of 83 kt NH }N yr ~1. Although export is larger than previously estimated, due to the larger 3 contribution of non-agricultural NH emissions, it is still insu$cient to balance the UK budget, for which around 150 kt 3 NH }N are estimated to be exported. The shortfall in the budget is, nevertheless, well within the range of uncertainty of 3 the total emissions. ( 2000 Elsevier Science Ltd. All rights reserved. Keywords: Ammonia; Emission inventory; Atmospheric budget; Sewage; Wild animals; Transport; Industry

1. Introduction It is well established that the major source of NH 3 emissions to the atmosphere is the volatilization from decomposing livestock waste, with the second major source being losses from agricultural plant canopies, particularly following the application of N fertilizers (e.g. Buijsman et al., 1987; Asman and van Jaarsveld, 1992; Sutton et al., 1995; Bouwman et al., 1997; Pain et al.,

* Corresponding author. Tel.: #44-131-445-4343; fax: #44131-445-3943. E-mail address: [email protected] (M.A. Sutton)

1998). In the UK it has been estimated that these contribute around 85% of the total NH emission (e.g. RGAR, 3 1997). Because of this, most experimental studies and inventories examining NH emissions have focused most 3 attention on these agricultural sources. Quantifying the magnitude of non-agricultural sources is more uncertain, since there is a wide range of source types, with often little underlying experimental data. Although very uncertain, the estimation of non-agricultural NH sources has become an area of debate since 3 atmospheric budget estimates have suggested that the existing emission estimates are not su$cient to balance deposition and atmospheric transport (e.g. Buijsman, 1987; Lee and Dollard, 1994; Sutton et al., 1995; Fowler et al., 1998). Ammonia emissions from non-agricultural

1352-2310/00/$ - see front matter ( 2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 9 9 ) 0 0 3 6 2 - 3

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M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

sources have therefore been addressed to see whether these might provide the missing term in the atmospheric NH budget. Recent estimates for the UK included those 3 of Eggleston (1992) of 63 kt NH }N yr ~1 and Lee and 3 Dollard (1994) of 56}60 kt yr ~1, both for 1990, equivalent to an emission of +1 kg NH }N per head of popu3 lation per year. In reviewing these and other data on non-agricultural sources, Sutton et al. (1995) estimated a total of 38 (14}73) kt N yr~1. The smaller estimate of the latter study re#ected reduced emission factors from the sources considered, while recognizing that uncertainties were very large. The present paper updates and extends the non-agricultural NH emission estimates of Sutton et al. (1995) 3 and scales these to the UK for a base year of 1996. While the focus is on deriving national totals, the paper is of general interest in providing emission factors for nonagricultural sources. Uncertainty limits are provided, taking the approach of Sutton et al. (1995) that these in most cases propagate reasonable limits in the input data rather than provide a formal measure of statistical precision. Sewage sludge spreading, biomass burning and agro-industry are included as these are not normally included in agricultural inventories, and have clear links to other source sectors. The following sections detail the di!erent source types and these are followed by a summary of the sources and comparison with other recent inventories.

2. Direct ammonia emissions from humans Direct NH emissions from humans (excepting sew3 age, Section 6) occur from breath, sweat and infant excretion. Ammonia emissions from cigarette smoking are also be included in this group. 2.1. Ammonia emissions from human sweat Ammonia emissions from human sweat were "rst suggested by Healy et al. (1970), who provided an upper estimate by assuming complete hydrolysis and volatilization of urea in sweat, estimated at 0.26 kg N person~1 yr~1. This estimate was subsequently used as the basis for sweat emissions by Cass et al. (1982), Eggleston (1992) and Lee and Dollard (1994). A smaller emission estimate was provided by Sutton et al. (1995), who suggested that only 20% would be volatilized. Applying a similar total N excretion estimate (Altman and Dittmer, 1968; Warn et al., 1990), the last study provided an emission factor of 0.04 kg NH }N person~1 yr~1. 3 The main justi"cation of NH emission from sweat 3 (and also from breath, see below) has been the observation of increased concentrations of NH in houses (e.g. 3 Atkins and Lee, 1993; Tidy and Cape, 1993). However, it should be noted that, due to the absence of measure-

ments of room ventilation rates, these studies have not been used to calculate the emission factors adopted. The key point underlying all the estimates of sweat NH 3 emissions is the estimate of Healy et al. (1970), which simply assumed that 5% of total N excretion occurs through sweat. Improved data on sweat N excretion are therefore central to reducing the uncertainties. In two experimental studies Czarnowski et al. (1995) and Columbani et al. (1997) measured sweat N excretion during exercise. Columbani et al. (1997) showed excretion rates of 140, 30 and 10 mg N person~1 h ~1 for urea, NH and amino acids, respectively. These values are 3 supported by the measurements of Czarnowski et al. (1995), whose results indicate NH excretion rates of 23 3 and 31 mg N h ~1 for subjects on normal and highprotein diets, respectively. Based on these results, a total N excretion in sweat of 180 (100}400) mg N person~1 h ~1 is adopted, with uncertainties from a literature review of Columbani et al. (1997). Information on exercise frequency for the UK is provided by OPCS (1994), which may be used to derive an average exercise duration of 2.2}4.3 h person~1 week~1. Much more uncertain is the number of hours of sweating during a week due to other causes, such as manual work and hot temperatures. In the present estimate this is assumed to equate to approximately 7 h exercise, providing a total of 10 h sweating person~1 (Table 1). Annual N excretion in sweat is estimated to be 94 (42}250) g N person~1 yr~1, which is smaller than the earlier estimates following Healy et al. (1970). In Table 2a distinction is made between hydrolysis and volatilization of the excreted N, providing an emission rate of 14 (2}75) g NH }N person~1 yr~1, which is more conserva3 tive than estimated by Sutton et al. (1995). 2.2. Ammonia emissions from human breath Emissions from human breath are estimated to be much smaller than from human sweat. Lee and Dollard (1994) calculated a "gure of around 0.1 kt NH }N yr~1 3 for the UK, which was adopted by Sutton et al. (1995). Further data are available to update this estimate, with a number of authors reporting NH concentrations in 3 human breath. The most reliable estimates (from complete sampling using exhalers) are those of Davies et al. (1997) who calculated a mean of 682 lg NH m~3 in 3 breath with a range from 302 lg m~3 (after fasting) to 1278 lg m~3 (after a protein meal). Other measurements reported by Moskalenko et al. (1996) at 71}178 lg m~3 may be low due to indirect sampling of the exhaled NH , 3 while Nielsen et al. (1997) reported a value of 2000 lg m~3, although no details were given. The values of Davies et al. (1997) compare well with earlier measurements of Nefedov et al. (1969), who estimated means of 560 and 760 lg m~3 for a smoker and non-smoker, respectively. This last study, and others noted below,

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

857

Table 1 Ammonia emissions from human sweat and breath, with estimates scaled to the UK Best estimate

Low estimate

180 10 93.6

100 8 41.6

400 12 249.6

Assumed % hydrolysis of sweat N Assumed % volatilization of sweat NH 3

75% 20%

50% 10%

100% 30%

Sweat NH emission (g N pers~1 yr~1) 3

14.04

2.08

74.88

UK sweat NH emission (kt NH }N yr~1) 0.82 3 3 Exhaled air concentrations (lg NH m~3) 682 3 Average breathing rate (l min ~1) 10

0.12 302 8

4.39 1278 14

Sweat N excretion (mg N pers~1 h~1) Sweating duration (h week~1) Sweat N excretion (g N pers~1 yr~1)

High estimate

Breath emission (g NH }N pers ~1 yr~1) 3

3.0

1.0

7.7

UK breath NH emission (kt NH }N yr~1) 3 3

0.173

0.061

0.454

showed that the breath of smokers does not contain signi"cantly more NH when not smoking. 3 Breathing rates vary greatly depending on the amount of physical exercise, from 5}10 l min~1 at rest (Green, 1972; Taverner, 1983; Clancy and McVicar, 1995) to 50}100 l min~1 during exercise (Green, 1972; Clancy and McVicar, 1995). An average estimate of 10 (8}14) l min~1 is applied here. Average breath NH emission (Table 1) is 3 estimated at 3 (1}8) g NH }N person ~1 yr~1, resulting 3 in a UK contribution of 0.17 (0.06}0.45) kt NH }N yr~1. 3 Although larger than the earlier estimate, it is clear that this is not a major source of regional NH emissions. 3 2.3. Ammonia emissions from smoking A number of studies have measured NH emissions 3 from cigarettes. Warn et al. (1990) reported an estimated 0.16 mg NH }N cigarette~1, which was the mean of two 3 short studies. More recently Cole and Martin (1996) provided a more extensive survey of "ve cigarette brands using a smoking machine giving a mean of 6.2 mg NH }N cigarette~1. The most detailed study has, how3 ever, recently been provided by Martin et al. (1997), who surveyed emissions of many chemical species for 50 cigarette brands using a smoker in an environmental test chamber. The mean of the results of Martin et al. (1997) is certainly the most reliable and is also midway between the other estimates at 3.4 mg NH }N cigarette~1. Error 3 limits are taken here at 1.7}6.2 mg cigarette~1. The average cigarette consumption in the UK is 5200 (cigarette smoker)~1 yr~1 (OPCS, 1994), with an estimated smoking population of 11.3 million (derived from OPCS, 1994; ONS, 1997). This provides a total of 0.2 (0.1}0.4) kt

Notes Columbani et al. (1997) Uncertainty assumes $50% high estimate is similar to that of Healy et al. (1970) Sutton et al. (1995), but smaller high estimate. Some NH absorbed 3 in clothes and buildings

Davies et al. (1997) Green (1972), Taverner (1983), Clancy and McVicar (1995)

NH }N yr ~1 for the UK, which is probably the most 3 reliable of the component NH emission estimates from 3 humans. 2.4. Ammonia emissions from infants It has sometimes been mentioned that excretion of N from infants may be a signi"cant contribution to NH 3 emissions since urine in nappies does not enter the sewage system and may hydrolyze giving high indoor NH 3 concentrations (Atkins and Lee, 1993; Lee and Dollard, 1994). Despite this, no quantitative estimates of NH 3 emissions from infants have been made. A guide to these emissions may be made by using estimates of N excretion, and reasonable assumptions regarding the fraction of excreted N that is hydrolyzed to NH and volatilized. 3 Sound data on infant excretion rates are available, with Jackson et al. (1981) and Steinbrecher et al. (1996) reporting 87 and 198 mg urea N kg~1 d~1, respectively. These are used here to provide uncertainty limits, with the mean of 142.5 mg N kg~1 d~1. It is assumed here that nappies are worn up to the age of 3, with decreased use at the end (Table 2). The most uncertain term is the percentage excreted N lost to the atmosphere. Informal reports of NH odour from nappies suggest that emis3 sions are smaller for disposable nappies than washable nappies, and it is noted that (5% infants in the UK still use washable nappies. It is clear that most of the excreted N remains in the nappies and an assumed volatilization rate of 3 (1}10)% is not unreasonable. Using these numbers, the main conclusion from Table 2 is that this represents only a very minor source of NH emission on a UK 3 scale, at 0.03 (0.01}0.14) kt NH }N yr~1. 3

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M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

Table 2 Ammonia emissions from infant nappies, with estimates scaled to the UK Best estimate N excretion (mg urea N kg~1 bodywt. d~1) 142.5 Annual urinary N excretion: (1 yr (kg child~1 yr~1) Annual urinary N excretion: 1}3 yr (kg child~1 yr~1) Estimated % volatilization of excreted urinary N: (1 yr Estimated % volatilization of excreted urinary N: 1}3 yr Estimated NH emission: (1 yr 3 (g NH }N child~1 yr~1) 3 Estimated NH emission: 1}3 yr 3 (g NH }N child~1 yr~1) 3 UK infant NH emissions (t NH }N yr~1) 3 3

Low estimate

High estimate

Notes

87

198

Jackson et al. (1981), Steinbrecher et al. (1996) Average weight 7.5 kg (CGF, 1993)

0.39

0.24

0.54

0.65

0.40

0.90

3

1

10

2

1

8

Average weight 12.5 kg (CGF, 1993)

11.7

2.4

54.2

% reduced to re#ect decreased nappy use For 734,000 children (ONS, 1997)

14.6

3.0

67.8

For 1,468, 000 children (ONS, 1997)

30.1

6.1

139.2

3. Horses and pets

3.2. Ammonia emissions from dogs

3.1. Ammonia emissions from horses

The most frequently used estimate of NH emissions 3 for dogs is that derived by Cass et al. (1982) at 2.07 kg NH }N animal~1 yr~1. This formed the basis for the 3 estimates of Eggleston (1992) and Lee and Dollard (1994). In contrast, Sutton et al. (1995) suggested that this would substantially overestimate emissions; Cass et al. (1982) assumed that 90% of the excreted urinary N would be volatilized, which is much larger than has been established for agricultural livestock. Assuming that 36% of the urinary N would be volatilized (by similarity to cattle), which is approximately equivalent to 25% volatilization of total N excretion, Sutton et al. (1995) estimated an emission rate for dogs of 0.81 kg NH }N dog~1 yr~1. 3 More recent data of Egron et al. (1996) have shown that a signi"cant quantity of NH is also present in faeces 3 (in addition to organic N), which is liable to volatilize. The total excretion of urinary N (Cass et al., 1982) and faecal NH (Egron et al., 1996) is estimated here at 3 2.6 kg N dog~1 yr~1. Comparison of NH emission 3 rates as a % of excreted available N with sheep and cattle shows smaller loss rates for free roaming animals, such as sheep, than for animals such as cattle which are partly housed and the waste stored. Bearing this in mind, the 25% volatilization rate of total N (or 36% as available N) assumed by Sutton et al. (1995) may be too high, and this is taken here as an upper estimate, with the sheep volatilization rate (Pain et al., 1998) taken as the lower estimate (Table 3). Average dog NH emissions are estimated at 3 0.6 (0.3}0.9) kg NH }N animal~1 yr~1, which equates to 3 4.4 (2.1}7.0) kt NH }N yr~1 for the UK. 3

Although horses are not generally used as agricultural animals in the UK, there is a large number mainly for pleasure riding and racing. ApSimon et al. (1987) provided the "rst UK estimate of horse NH emissions, 3 which was based on a performance race horse (ApSimon pers. comm. 1993), at 31.6 kg NH }N animal~1 yr~1. 3 Estimates for pleasure riding horses show close agreement between 8 kg N animal~1 yr~1 (Buijsman et al., 1987) and 15.0 kg N animal~1 yr~1 (MoK ller and Schieferdecker, 1989). Other estimates are Asman and van Jaarsveld (1992) (10.3), ECETOC (1994) (9.8). Sutton et al. (1995) applied an average value of 10 (5}20) kg NH }N animal~1 yr~1, and this is also applied here for 3 pleasure riding horses. There are a signi"cant number of competition horses, and it is relevant to distinguish these in the total. Given an average racehorse body weight of 500 kg and daily food intake of 2.5% of body weight (Hanson et al., 1996), and assuming a feed N content of 3%, provides a total N excretion of 137 kg N animal~1 yr~1. By comparison with cattle, around 25% of the total excreted N is expected to be volatilized as NH (Sutton et al., 1995; Pain 3 et al., 1998). With estimated uncertainties, this gives a race horse emission of 33.7 (15}40) kg NH }N ani3 mal~1 yr~1, very close to the estimate of ApSimon et al. (1987). Overall the total estimated UK horse NH emis3 sion is 7.5 (3.5}12.7) kt NH }N yr~1, with approximately 3 30% deriving from race horses.

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

859

Table 3 Ammonia emissions from dogs and cats, with estimates scaled to the UK Best estimate

Low estimate

High estimate

Notes

*

*

88% urinary N, 12% faecal NH x

24%

11%

36%

Lower and upper % losses by comparison to sheep and cattle, respectively

Ammonia emission (kg NH }N dog~1 yr~1) 3 UK dog population (million)

0.61 7.2

0.30 6.9

0.93 7.5

Total UK emission from dogs (kt NH }N yr~1) 3 Estimated N excretion: cats

4.4

2.1

7.0

Estimated N excretion: dogs (kg available N dog~1 yr~1) % volatilization of available N

(kg urinary N cat~1yr~1) % volatilization of urinary N

2.6

0.91

*

Ammonia emission (kg NH }N cat~1 yr~1) 3 UK cat population (million)

0.11 7.9

0.05 7.7

0.16 8.1

Total UK emission from cats (kt NH }N yr~1) 3

0.9

0.4

1.3

Available data for emissions from agricultural sources show larger % volatilization losses in proportion to the magnitude of the source. Hence large % losses are found for housed poultry, where the waste is collected together, while smaller % losses are found for grazing sheep. The

comm.

By comparison to dogs, but assuming 50% waste buried (Sutton et al., 1995)

18%

4. Wild animals and sea birds

(pers.

Given a 5 kg cat and excretion rates of Hendriks et al. (1997)

6%

Ammonia emissions from cats were estimated by Cass et al. (1982) at 0.66 kg N cat~1 yr~1, again assuming 90% volatilization of the excreted N (estimated at 0.73 kg N cat~1 yr~1 for a small 2.5 kg cat). This value formed the basis of the estimates of Eggleston (1992) and Lee and Dollard (1994). In contrast, Sutton et al. (1995) again applied a smaller volatilization rate, at 18% of urinary N, since it was assumed that 50% of the excreta would be buried. Following the same approach used for dogs in Table 3, cat emissions are calculated here using updated excretion estimates. Hendriks et al. (1997) reported a urinary excretion rate of a cat on a normal diet of 500 mg kg~1 body weight d~1, which for a typical 5 kg cat equates to 0.91 kg urinary N cat~1 yr~1. Ammonia emissions are estimated at 0.11 (0.05}0.16) kg NH }N cat~1 yr~1, pro3 viding a UK emission of 0.9 (0.4}1.3) kt NH }N yr~1. 3

SSPCA

*

12%

3.3. Ammonia emissions from cats

RSPCA, 1998)

RSPCA, 1998)

SSPCA

(pers.

comm.

physical basis is that a larger fraction of emission can be retained by soil and vegetation for smaller individual sources. By this reasoning, it is expected that emissions from small dispersed wild animals are expected to be negligible, with most emission recaptured within plant canopies. The present estimates therefore only consider emissions from larger or colony forming animals. Values for deer and sea birds (Sutton et al., 1995) are reassessed, and new estimates made for badgers, foxes, feral cats and rabbits. 4.1. Ammonia emissions from wild animals Sutton et al. (1995) estimated emissions from red deer (0.9 kg N animal~1 yr~1), assuming an emission rate at 2.5 times that of a sheep based on di!erential grazing rates. If this estimate is updated for current estimates of sheep emissions (Pain et al., 1998), then a revised estimate is 1.23 kg N animal~1 yr~1. Other kinds of deer may also be considered, making a separation between large deer, equivalent to 2.5 sheep (red, sika and fallow deer), and small deer, equivalent to 1 sheep (roe, muntjak). Given 471,000 and 540,650 large and small deer, respectively (Yalden, 1998), and assuming a factor of 2 uncertainty, provides a UK total of 0.8 (0.4}1.6) kt NH }N yr~1. 3 Although emissions from small animals such as rabbits are not expected to be large, with most recaptured within canopies, the very large number of rabbits in the UK

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M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

indicates that this source could be signi"cant. The combined population of rabbits and hares in the UK is estimated at 38.7 million $50% (DOE, 1996). In terms of grazing rates and hence excretion, approximately 14 rabbits are equivalent to 1 sheep (H. Armstrong, Scottish Natural Heritage, pers. comm.). By reference to current best estimates of sheep emissions (Pain et al., 1998), and assuming that the % volatilization rate is half that of sheep, rabbit NH emissions are estimated at 17 3 (8.6}34) g NH }N animal~1 yr~1. This scales to 0.68 3 (0.17}2.1) kt NH }N yr~1 over the UK. 3 A small amount for the most abundant other large wild animals may be added to rabbit emissions: feral cats, badgers and foxes, of which there are an estimated 810, 250 and 240 thousand each in the UK, respectively (DOE, 1996). The estimate for feral cats follows that for domestic cats, while the estimate for badgers and foxes assumes an emission rate 50% (30}70%) that for sheep, giving 0.24 (0.15}0.34) kg NH }N animal yr~1. Overall 3 the total UK emission for these species is estimated at 0.22 (0.07}0.48) kt NH }N yr~1. 3

in central Scotland, holding an estimated 50,000 birds. Excretion rates based on "eld metabolic rates were much larger than for sedentary housed poultry, and estimated at 3.08 kg N bird~1 yr~1 on the colony. The mean NH air concentration measured at the site was 806 3 (30}1330) lg m~3 for a monthly sampling period while the birds were present at full density. Using a dispersion model these air concentrations were found to be consistent with emissions of 83% of N excreted on the colony. Further measurements, after some of the birds had left, provided smaller concentrations up to 300 lg m~3, indicating that the emissions might be smaller in other periods, although some sampling uncertainties remain with these later measurements. Comparison with emission rates for housed birds such as turkeys, under high emission management with manure not dried, imply emission rates of around 70% of the excreted N (Pain et al., 1998; Pain, pers. comm. 1998), and this provides some support for the larger emission rates calculated here. In calculating emissions from large seabirds here, a best estimate of NH loss of 70% is assumed (Table 4). 3 For other sea birds, comparison of "eld metabolic rates (Birt-Friesen et al., 1989) suggests excretion rates are 20% of those for large seabirds (cf. to 33% estimated by Sutton et al., 1995). This provides emission estimates of 2.2 (1.0}3.6) and 0.24 (0.07}0.6) kg NH }N bird~1 yr~1 3 for large and small birds, respectively. The large magnitude relative to other sources is due to very high "eld metabolic rates, high dietary N content and large estimated % volatilization rates from N excreted on colonies. Scaled to the UK, sea bird emissions account for an estimated 3.4 (1.2}7.0) kt NH }N yr~1. Sea bird NH 3 3 emissions may be particularly important where they occur in remote areas with otherwise very few sources.

4.2. Ammonia emissions from sea bird colonies Emissions of NH from sea bird colonies were esti3 mated by Sutton et al. (1995) at 0.3 kg NH }N bird~1 3 for large birds (gannets, shags, cormorants) and 0.1 kg bird~1 yr~1 for other colony birds. Bird numbers were taken from available estimates for the 1970s, while the emission rates were based on rough similarity to housed poultry. Recent information suggests both that sea bird numbers have increased signi"cantly and that the emission estimates used were too small. BoK ttcher (1996) made an initial "eld study of NH 3 concentrations and emission rates from a gannet colony

Table 4 Ammonia emissions from sea bird colonies, with estimates scaled to the UK Best estimate

Low estimate

High estimate

Excretion of N on colony: large sea birds (kg N bird~1 yr~1) Excretion of N on colony: other sea birds (kg N bird~1 yr~1)

3.08

2.37

4.00

0.35

0.18

0.62

% emission from N excreted on colonies large sea bird emission (kg NH }N 3 bird~1 yr~1) other sea bird emission (kg NH }N 3 bird~1 yr~1)

70% 2.15

40% 0.95

90% 3.60

0.24

0.07

0.55

Total UK seabird emissions (kt NH }N 3 yr~1)

3.44

1.24

7.01

Notes Assumes 50% occupancy for 6 months/year Assumes 38% occupancy for 4.5 months/year. Excretion 20% that of large birds For 648,000 birds!: gannet, shag & cormorant For 8,449,000 birds!: gulls, fulmars, kittiwakes, razorbills, guillimots, pu$ns, terns & skuas

!Lloyd et al. (1991), Thompson et al. (1997), adjusted to UK and multiplied by 1.32 to include non-breeders (Cairns et al., 1991).

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

5. Biomass burning and natural ecosystems Little new information is available on UK emissions of NH from biomass burning. Lee and Atkins (1994) 3 estimated an emission of 3.3. kt NH }N for agricultural x stubble burning in 1991, but noted that this would decline in subsequent years due to burning restrictions. Reviewing other data on biomass burning (including natural and agricultural vegetation), Sutton et al. (1995) estimated an emission of 1.6 (0.2}6.6) kt NH }N yr~1, x and this estimate is applied here. It should be noted that moorland burning (&muirburn') is still a major practice in the Scottish highlands, although there are no known measurements of emissions from this source. Sutton et al. (1995) also consider the extent of NH 3 emissions from semi-ecosystems. Measurements show that while emissions may occur for short periods, net #uxes are toward deposition for UK ecosystems. These bi-directional exchange processes are treated in de"ning net dry deposition and therefore not included here. Earlier inventories (e.g. Buijsman et al., 1987; Eggleston, 1992) have sometimes referred to these #uxes as emissions from &natural soils', although it is noted here that the net #ux is generally more a!ected by interactions with overlying plant canopies.

6. Sewage and land5ll Emissions from sewage may arise from waste water treatment works (particularly anaerobic processing) and from spreading of treated sewage onto agricultural land. Available data on both sources were reviewed by Sutton et al. (1995), who estimated UK 1990 emissions of 9.1 (2.5}16.5) and 1.2 (0.7}2.5) kt NH }N yr~1 for sewage 3 spreading and treatment, respectively. More recent data of NH emissions of sewage spread3 ing provide support for some of the estimates used by Sutton et al. (1995), although the total emission is estimated to be smaller than the earlier estimates. In experimental studies Harmel et al. (1997) found an average volatilization of 27% N applied (compared with 25% adopted by Sutton et al. (1995) for digested sewage sludge with a N content of 5.2% of dry solids (compared with 6% adopted by Sutton et al.). In contrast, it is noted here that around 60% of sewage sludge is injected rather than surface spread (Environment Agency, 1997; B. Chambers, ADAS, pers. comm.). Assuming that injection reduces emissions by 75% (e.g. TFEI, 1996), an emission rate of 16.25 (3}9)% of N applied is used here for the fraction injected. This revision has a large e!ect on the estimated emission, which equates to 5.4 (1.5}10.2) kt NH }N yr~1, compared 3 with 14.5 (4.1}26.2) kt yr~1 if 100% surface spreading were assumed. It may be noted that the activity of this source has increased by 60% since 1990 as dumping

861

of sewage sludge at sea has been gradually phased out (DOE, 1993; DETR, 1997). Ammonia emissions from sewage treatment plants are particularly uncertain, with the only estimates being those of Lee and Dollard (1994) and Sutton et al. (1995), both being based on experimental data of Lee et al. (1992) for one activated sludge treatment works. Uncertainties were recognized in the passive sampling methodology, with Sutton et al. (1995) dividing the recorded NH 3 concentrations by a correction factor of 2, resulting in the estimated emission noted above. More recent tests with passive NH samplers of the kind used by Lee et al. 3 (1992) indicate that the correction factors may be only appropriate at small concentrations ((5 lg m~3), although this is highly operator speci"c (unpublished data). Bearing this in mind, the upper estimate is revised here to 4.9 kt NH }N yr~1, with the note that further measure3 ments are required. It is well established that municipal refuse contain signi"cant quantities of "xed N, with Burton and Watson-Craik (1998), for example, estimating a value of 0.5% N. However, there is very little information on gaseous emissions of NH from land"ll, with the only estimate 3 being that of Eggleston (1992) of 3.3 kt NH }N yr~1, 3 which was adopted with a factor of 2 uncertainty by Sutton et al. (1995). The estimate is based on the conclusions of Munday (1990) that nitrogenous emissions equate to 7.3% of methane emissions, with 10% of the emitted N being in the form of NH . In the absence 3 of other estimates, it is clear that this source is highly uncertain and that more measurements are required.

7. Industrial sources The most frequently cited sources of industrial NH 3 emissions are manufacture of NH and N containing 3 fertilizers. The estimates of MHPPE (1983) have been used by a number of authors providing UK emissions of around 7 kt NH }N yr~1 (e.g. Buijsman et al., 1987; 3 Eggleston, 1992; Lee and Dollard, 1994). A smaller estimate of 1.6 kt NH }N yr~1 was made by ECETOC 3 (1994) based on new information from the International Fertilizer Association and this was adopted by Sutton et al. (1995). The validity of these general estimates may now, to some extent, be checked due to the recent availability of the Chemical Release Inventory (CRI) for England and Wales, developed under UK Integrated Pollution Control (IPC), and being further updated under the EU Directive on Integrated Pollution Prevention and Control (IPPC). Detailed emissions are provided on an installation basis for all processes requiring authorisation. The numbers reported are a combination of measurements and estimates. Since NH is a minor in3 dustrial pollutant compared with NO , SO , etc. it is x 2

862

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

Table 5 Ammonia emissions from industrial sources registered in the UK chemical release inventory Source

Fuel and power production Metal production and processing Mineral industries Chemical industry Manufacture and use of organic chemicals Inorganic chemical processes Chemical fertilizer production Petrochemical, acid and halogen processes Waste disposal and recycling Paper/pulp manufacture, coating and printing All recorded industry: England & Wales 1996 All recorded industry: UK 1996!

Best estimate (t NH }N yr~1) 3 163 351 261 1651 2436 2952 128 0.05 3.4 7915 8953

agree very closely. Peters (1994) in the Netherlands estimated an emission of 0.082 kg NH }N t~1 fresh beet 3 processed. This compares with 0.101 Kg t~1 reported for an Italian processing plant by Carlesso and Marani (1995), and 0.080 kg t~1 reported by Sullivan et al. (1997) in the USA. The average of these, at 0.088 kg NH }N t~1 3 is taken as the best estimate here. In the UK around 10.5 Mt (fresh weight) of sugar beet are processed (at nine locations), providing an estimated total of 0.9 (0.6}1.2) kt NH }N yr~1, assuming an uncertainty of $30%. Al3 though a small source in relation to national totals, the limited number of processing plants indicates that these emissions would be very important locally.

8. Transport !Scaled from England and Wales by population ratio of 1.13.

likely that in many cases NH emissions have not been 3 registered, so that the numbers re#ect minimum estimates. Table 5 shows the wide range of registered IPC processes contributing to NH emissions, with the total 3 emission estimated at 8.95 (8.95}13.4) kt N yr~1, assuming an upper uncertainty of #50%. Apart from uncertainties in the registered processes included in the CRI (IPC Part A processes), it is likely that there are many other industrial NH sources under local authority con3 trol (Part B processes), which are not recorded in the CRI. It is clear that measurements of NH emissions 3 from such sources would be valuable. Probably the most signi"cant other industrial source not included above is the processing of sugar beet for sugar production. Several studies have measured NH 3 emission rates from sugar beet processing, and these

Emissions of NH from vehicles were previously esti3 mated to be rather small, lying in the range 0.2}1.4 kt NH }N yr~1 (Eggleston, 1992; Lee and Dollard, 1994; 3 Sutton et al., 1995). The underlying measurements were for normal petrol and diesel engines. Recently, however, Strogies and Kallweit (1998) and TFEI (1996) have noted that petrol vehicles "tted with catalytic converters may provide much larger NH emissions, the latter citing the 3 work by de Reydellet (1989) and Volkswagen AG (1989). Of the two original reports, only that of Volkswagen AG actually described relevant measurements, and it was these which were adopted by TFEI (1996) for application to European emission inventories. TFEI (1996) did not provide uncertainty limits, and these are taken here (Table 6) as $1 standard deviation from the experimental studies of Volkswagen AG (1989). Table 6 also shows estimated emissions from other vehicle types. Scaled for vehicles usage in the UK this provides an estimated 8.9 (3.3}14.5) kt NH }N yr~1, of which 94% is 3

Table 6 Ammonia emissions from transport sources, with estimates scaled to the UK

Emission factors (mg NH }N km~1) 3 Petrol car#catalytic converter Petrol car, no catalytic converter Diesel car Average motorcycle Average LGV Average: HGV (inc. buses & coaches) Total UK vehicle NH emissions (kt NH }Nyr~1) 3 3

Best estimate

Low estimate

High estimate

Notes

70.3 1.8 1.0 1.2 1.0 2.4

25.3 1.2 0.3 0.9 0.5 0.8

115.3 2.3 1.7 1.8 1.8 4.9

!, 118,509 million km# !, 211,654 million km# !, 39,633 million km# ", 4,286 million km# ", 41,633 million km# ", 36,224 million km#

8.88

3.33

14.49

!From Volkswagen AG (1989), with uncertainties $1 SD of experimental data. "Means of classes from TFEI (1996), with uncertainties scaled relative to cars. #Estimated km driven for 1996, from UK vehicle numbers and usage provide by DETR (transport statistics, pers. comm.).

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

due to cars with catalysts and 4% due to other petrol cars, with all other vehicles only contributing 2%. This highlights the reliance of the total on the results of Volkswagen AG (1989). Although comprehensive tests were carried out (using three di!erent test cycles per car), the statistics of catalytic converter emissions are based on a sample of only seven cars (three Audi and four Volkswagen), representing three models. Given the size of the calculated emission, and the fact that use of catalytic converters will increase over the next 10 yr, it is clear that further measurements are warranted. If 90% petrol vehicles had been "tted with catalytic converters, the total UK vehicle NH emissions would have been 21 3 (7.6}35) kt NH }N yr~1. 3 The "ndings of the controlled measurements for speci"c engine types of Volkswagen AG (1989) are supported by recent measurements by Fraser and Cass (1998) of NH total emissions from roadway tunnel. They inferred 3 an emission rate which was equated to an estimated 59 mg NH }N km~1 for cars "tted with catalytic con3 verters. A key point mentioned by Fraser and Cass (1998) is that poorly operating or malfunctioning catalytic converters may provide much larger NH emissions 3 (Dickson, 1991).

9. Coal combustion and waste incineration Emissions of NH from coal combustion were re3 viewed by Lee and Dollard (1994), who concluded that the most signi"cant emissions would arise from domestic coal combustion, with the most reliable emission estimate being that of Geadah (1985) at 0.82 kg NH }N t~1 3 coal burned. Sutton et al. (1995) adopted this value assuming an uncertainty of a factor 2, and in the absence of further data it is also applied here. In scaling to the UK, it may be noted that coal domestic burning has decreased substantially from 4.3 Mt for around 1990 (DoE, 1990) to 2.7 Mt for 1996 (DTI, 1997). Applying this to estimate UK emissions provides 2.2 (1.1}4.4) kt NH }N yr~1. It 3 may be noted that coal combustion in power stations is more e$cient, giving much smaller emissions. For a total non-domestic UK coal combustion of 68.7 Mt in 1996, applying emission estimates of Bauer and Andren (1985) (0.23 g NH }N t~1), represents an emission of only 16 t 3 NH }N yr~1. 3 Lee and Dollard (1994) also reviewed available data on NH emissions from waste incineration, identifying esti3 mates from Miner (1969) and Geadah (1985) of 0.2 and 0.14 kg NH }N t~1 combusted waste. Scaled to the UK 3 they estimated emissions in the range 0.6}0.9 kt NH }N, 3 for which Sutton et al. (1995) suggested an uncertainty of $ a factor of 2, providing an emission factor of 0.17 (0.09}0.26) kg NH }N t~1 waste. The estimate for 1990 3 may be scaled for increased amounts of incineration in 1996. Total UK wastes have been estimated at 414 Mt

863

(DETR, 1997). However, it is assumed here that incineration is only a possibility for municipal wastes, sewage sludge, commercial waste, and &other industrial' waste, which account for 105.3 Mt. (Classes not included are agriculture, mining and quarrying, dredged spoils, demolition and construction, power station ash and steel manufacturing). Of municipal waste (29 Mt), 7.6% is incinerated (DETR, 1997), and this "gure is around 22% for sewage sludge (1.3 Mt dry solids). The most uncertain amount is the fraction of commercial and other industrial waste (75 Mt) that is incinerated. It is assumed here that this is incinerated half as frequently as municipal waste at 3.8 (1.9}7.6)%. Combining these "gures indicates 5.3 (3.9}8.2) Mt combusted waste, equivalent to an emission of 0.91 (0.33}2.1) kt NH }N yr~1. 3 10. Household products and non-agricultural fertilizer use Although NH is a known component of many house3 hold products, studies have rarely estimated emissions from these sources. An exception is the inventory for the Netherlands of Erisman (1989), which estimated an average household use of 1 l household~1 yr~1 NH solution 3 as a cleaning agent. In the present study, a market survey was made of products containing NH with estimated 3 usage. Potentially signi"cant sources identi"ed were garden fertilizers, hair perming solutions, cleaning solutions (general, oven and window), latex screeding solution and refrigerants. Using best estimates of consumption rates (0.01}0.1 l household~1 yr~1) for di!erent cleaners and perming solutions, typical NH contents (2.5}10%) 3 and estimated emission rates (10}50%), UK NH emis3 sions from hair perming and cleaning solutions were estimated to be very small, in total 75 (5}870) t NH }N yr~1. The largest NH solvent source was esti3 3 mated for #oor screeding latex solution. Based on information from the industry, a UK consumption of 20 (10}40) kt solution yr~1 was estimated. Assuming an average NH content of 10%, with an emission of 50 3 (30}90)%, provides a total emission of 0.82 (0.25}2.97) kt NH }N yr~1. 3 Ammonia emissions from refrigerators were estimated assuming a UK stock of 3 (2}4) kt refrigerant NH , 3 and 5 (3}8)% leakage per year, based on information supplied by the industry. This equates to an estimated emission of 0.12 (0.05}0.26) kt NH }N yr~1. 3 Emissions from the use of fertilizers in the domestic market (for gardens and parks), were estimated assuming a volatilization rate of 2.5 (1}4)% of applied N (cf. Sutton et al., 1995). The UK consumption of garden fertilizers for 1996 is estimated at 61 kt (Datamonitor, 1998) with uncertainties estimated here in the range 50}80 kt. Assuming an average of 15% N content provides an emission of 0.23 (0.08}0.480) kt NH }N yr~1. 3

864

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

11. Discussion 11.1. Total non-agricultural ammonia emissions in the UK A detailed breakdown of estimated emission rates and UK contributions of the di!erent non-agricultural sources of NH identi"ed is given Table 7. The total non3 agricultural emission is estimated at 53.8 (26.9}106.4) kt NH }N yr~1, which equates to 65.4 (32.7}129) kt NH 3 3 yr~1. Several UK sources have been quanti"ed for the "rst time, including infant emissions, small deer and other major wild animals, sugar beet processing and other industrial sources, household products (solvents and refrigeration), and garden fertilizers. Mostly these new sources are minor, although combined they amount to 9.0 (7.0}17.4) kt NH }N yr~1. 3 The present estimates are summarized into a smaller number of emission classes for comparison with other

literature estimates in Table 8. The previous estimates were generally for a base year of 1990, compared with 1996 here. Table 8 therefore indicates where the changes in the present inventory are due either to changes in emission estimation (average emission factors), or to changes in the source activity between 1990 and 1996. Key elements for which the emission rate estimates are now smaller are direct human emissions (sweat, breath, smoking, infants), pets (cats and dogs), sewage and, compared with Eggleston (1992) and Lee and Dollard (1994), fertilizer production. In the case of emissions from humans and pets, Sutton et al. (1995) estimated much smaller emissions than the earlier authors. The revised estimates support this, and provide even smaller emissions. It may be noted that there has been some discussion in the literature about indoor measurements of NH concentrations as evidence 3 of humans being a source of NH (e.g. Atkins and Lee, 3

Table 7 Ammonia emissions from non-agricultural sources, with estimates scaled to the UK

Source

Average emission factor (units as NH }N) 3

Human breath Human sweat Infants emissions 0}3 yr! Cigarette smoking Race horses Other horses Pet dogs Pet cats Wild deer (large) Wild deer (small)! Other major wild animals! Large seabirds Other seabirds Biomass burning Ecosystems Sewage works Sewage spreading Land"ll Fertilizer manufacture Sugar beet processing! Other industrial sources! Transport Domestic coal combustion Industrial coal combustion Waste incineration Appliances & household products! Non-agricultural fertilizers!

3.0 (1.0}7.7) 14.0 (2.1}74.9) 13.7 (2.8}63.2) 17.8 (8.9}39.1) 33.7 (15}40) 10.0 (5}20) 0.61 (0.30}0.93) 0.11 (0.05}0.16) 1.23 (0.61}2.45) 0.49 (0.25}0.98) * 2.15 (0.94}3.60) 0.24 (0.07}0.55) * * * * * 0.09 (0.06}0.11) * * 0.82 (0.41}1.65) 0.23 (0.004}4.1) * * *

g person~1 yr~1 g person~1 yr~1 g infant~1 yr~1 g smoker~1 yr~1 kg animal~1 yr~1 kg animal~1 yr~1 kg animal~1 yr~1 kg animal~1 yr~1 kg animal~1 yr~1 kg animal~1 yr~1 * kg bird~1 yr~1 kg bird~1 yr~1 * * * * * * kg t~1 fresh beet * * kg t~1 coal burned g t~1 coal burned * * *

Total

*

*

!Included for the "rst time in the UK inventory. "British Horse Soc. (pers. comm.).

Population (thousands)

UK emissions (kt NH }N yr~1) 3

58,600 58,600 2,202 11,251 68" 497" 7,200 7,900 471 541 39,969 648 8,449 * * * * * 10.5 Mt yr~1 * * 2.7 Mt yr~1 68.7 Mt yr~1 * * *

0.17 (0.06}0.45) 0.82 (0.12}4.39) 0.03 (0.01}0.14) 0.20 (0.10}0.44) 2.3 (1.0}2.7) 5.0 (2.5}9.9) 4.4 (2.1}7.0) 0.9 (0.4}1.3) 0.6 (0.3}1.2) 0.3 (0.1}0.5) 0.9 (0.2}2.5) 1.4 (0.61}2.3) 2.1 (0.62}4.7) 1.6 (0.2}6.6) 0 1.2 (0.7}4.9) 5.4 (1.5}10.2) 3.3 (1.6}6.6) 3.3 (3.3}5.0) 0.9 (0.6}1.2) 5.6 (5.6}8.4) 8.9 (3.3}14.5) 2.2 (1.1}4.4) 0.02 (0.00}0.28) 0.9 (0.3}2.1) 1.0 (0.3}4.1) 0.2 (0.08}0.5)

*

53.8 (26.9}106.4)

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

865

Table 8 Comparison of selected literature estimates of UK non-agricultural NH emissions 3 Source Base year

Eggleston (1992) 1990

Lee & Dollard (1994) 1990

Sutton et al. (1995) 1990

Direct human emissions Horses Pets (cats & dogs) Wild animals (animals & seabirds) Biomass burning Ecosystems (natural soils) Sewage (works & landspreading)

14.0 4.3 15.6 * * 9.9 3.3

11.5 * 19.8 * * * 11.5}15.6

2.5 5.8 7.2 0.8 1.6 0 10.3

Land"ll sites Agro-industry (fertiliser production) Agro-industry (sugar beet processing) Other industrial sources Transport Coal combustion Waste incineration Household products Non-agricultural fertilizer use

3.3 12.4 * * 0.2 * * * *

* 7.4 * * 1.4 3.5 0.6}0.9 * *

3.3 1.3 * * 0.8 3.5 0.7 * *

Total

63

56}60

38 (14}73)

(0.6}5.8) (2.5}10.7) (2.5}9.9) (0.2}1.6) (0.2}6.6) (3.1}19) (1.6}6.6) (0.7}2.7)

(0.4}1.6) (1.6}6.6) (0.3}1.6)

New estimates (1998) 1996 1.2 7.3 5.3 5.2 1.6 0 6.6

Changes in new estimates

(0.4}5.4) (3.5}12.7) (2.5}8.3) (1.9}11.4) (0.2}6.6)

EF decreased EF increased EF decreased EF increased

(2.2}15.1)

EF decreased (SA increased)

3.3 (1.6}6.6) 3.3 (3.3}5.0) 0.9 (0.6}1.2) 5.6 (5.6}8.4) 8.9 (3.3}14.5) 2.2 (1.1}4.7) 0.9 (0.3}2.1) 1 (0.3}4.1) 0.3 (0.02}2)

EF decreased EF increased EF increased SA increased SA decreased SA increased EF increased EF increased

54 (27}106)

Notes: EF"average emission factor, SA"source activity.

1993; Tidy and Cape, 1993), although these studies were not amenable to calculation of emissions rates, due to the absence of measured ventilation rates. With small samples, both these studies showed similar enhancements of air concentrations due to the presence of either smokers or babies, with air concentrations increasing by around 60% with a baby or 300% with smokers. Of the human NH emissions estimates here, smoking is probably the 3 best estimated, with emissions per person larger than either breath or sweat (Table 7). This therefore provides a reference to scale the other human NH sources. As the 3 indoor NH measurements above showed the highest 3 concentrations in the presence of smokers, this supports the present small estimates sweat, breath and infant emissions. If the larger sweat emission NH rates following 3 Healy et al. (1970), Cass et al. (1982), Eggleston (1992) and Lee and Dollard (1994) had been correct, then indoor NH air concentrations would be little a!ected by smok3 ing. The component human NH emission factors in 3 Table 7 may be used to construct simple scenarios of household emissions for di!erent occupants. Using the present estimates, the presence of two average smokers in a house of four people would typically increase emissions (and therefore concentrations) by around 40% depending on indoor emission activities assumed. Using the same assumptions, but with the sweat NH emission rate 3 of Healy et al. (1970), two smokers would only increase concentrations by 3%.

Although estimated emission rates from sources treated by Eggleston (1992) and Lee and Dollard (1994) have been reduced here, Table 8 nevertheless indicates a similar total to that estimated by these authors. This is due to other new sources being identi"ed and as well as some increases in source activity since 1990. Larger emission rate estimates are calculated here for horses, wild animals and sea birds, industry (excepting fertilizer production) and household products. The largest changes are for sea birds, wild animals and industry. New data suggest that sea bird NH emissions may be very large 3 per bird, due to the very high N diets and large % volatilization rate. In addition, while not previously included, the very large number of rabbits in the UK (38 million) provided a signi"cant extra term. Key NH sources for 3 which activities have increased between 1990 and 1996 are transport (due to increased use of catalytic converters) and sewage spreading emissions (due to new restrictions on dumping at sea). In the case of sewage spreading, however, the resulting emissions are smaller than previously estimated, due to account being taken for the widespread use of waste injection in this sector. If total non-agricultural emissions were calculated for 1990 using the current methodology, the nonagricultural emission would be around 47 (25}96) kt NH }N. The net increase of 7 kt yr~1 between 3 1990}1996 is largely due to the increased use of catalytic converters.

866

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

11.2. Major uncertainties and recommendations for future research As an aid to summarizing future research needs, the major source groups are ranked in Table 9 according to the uncertainty range of the estimates. The largest source and largest uncertainty attaches to human sewage processing and land spreading. The larger of the two sources is estimated to be sewage spreading, and it is clear that further measurements are required. However, it must be noted that the information on sewage treatment emissions is extremely sparse and would warrant more detailed investigation. Transport NH emissions provide the second largest 3 estimated uncertainty, and this clearly needs further research. It has been noted here that this estimate is almost completely dependent on one study estimating emissions from catalytic converters (Volkswagen, 1989), for just three models and seven cars. The extent to which the emissions vary for other car brands and catalytic converters needs to be tested. The third major research requirement is for measurements of NH emissions from wild animals and sea birds. 3 In particular this needs to be focused on the emissions from sea birds as these contribute 2/3 of the emission. It should also be noted that sea bird colonies occur mostly in northern and western parts of the UK were agricultural NH emissions are small, so that these are expected 3 to have a relatively more important role in de"ning total emissions for these areas. Uncertainties for emissions from horses are only slightly smaller than for wild animals and sea birds, and also warrant further investigation. A key element here is the development of more reliable and precise estimates of

horse N excretion, as well as measurements of emissions from the waste of housed animals. Together these four categories account for around 50% of the total emission and uncertainty. The other sources noted in Table 9 have smaller uncertainties and are therefore lower priorities for research. Bearing in mind the progress that could easily be made in di!erent areas, however, some areas may be mentioned. Industrial sources, although not estimated to be highly uncertain, account for around 10 kt NH }N yr~1. A key question 3 here is the extent to which NH emissions from processes 3 have been under-recorded. A full survey would be a major task, but could be initiated by comparisons within the CRI between similar industries reporting or not reporting emissions. Finally, the estimate on NH emissions 3 from land"ll is based on only one study, and this could easily be improved by coupling measurements of NH to 3 studies of land"ll methane emission. 11.3. Contribution of non-agricultural sources to the UK ammonia budget It has often been noted from atmospheric budget studies that there appear to be insu$cient estimated NH 3 emissions to balance estimates of wet and dry deposition (e.g. Buijsman, 1987; RGAR, 1997; Fowler et al., 1998; Singles et al., 1998). Estimates of the UK budget were reported by RGAR (1997). Total emissions were estimated at 260 kt NH }N yr~1 (1993), based on 225 kt 3 from agricultural sources (cf. Pain et al., 1998; Cowell and ApSimon, pers. comm., 1995) and 35 kt from non-agricultural sources (cf. Sutton et al., 1995). This compared with a total deposition of 230 kt NH }N yr~1, x with 110 kt dry deposition and 120 kt wet deposition.

Table 9 Sources of non-agricultural NH emissions in the UK ranked by uncertainty ranges 3 Source

Sewage works & sewage spreading Transport Wild animals & sea birds Horses Biomass burning & ecosystems Pets (cats & dogs) Humans Industrial sources (inc. agro-industry) Land"ll Household products & misc. "rtelizers Coal combustion Waste incineration Total

UK emissions (kt NH }N yr~1) 3 6.6 8.9 5.2 7.3 1.6 5.3 1.2 9.9 3.3 1.3 2.2 0.9

(2.2}15.1) (3.3}14.5) (1.9}11.2) (3.5}12.7) (0.2}6.6) (2.5}8.3) (0.3}5.4) (9.6}14.6) (1.6}6.6) (0.4}4.6) (1.1}4.7) (0.3}2.1)

53.8 (26.9}106.4)

Range

Research priority

12.9 11.2 9.3 9.2 6.4 5.8 5.1 5.0 5.0 4.2 3.6 1.8

XXXX XXXX XXX XXX XX XX XX XX XX XX X X

79.5

X

M.A. Sutton et al. / Atmospheric Environment 34 (2000) 855}869

Accounting for an estimated import of 30 kt NH }N yr~1, x this only allowed an export (calculated by di!erence) of 30 kt yr~1. In contrast, estimates by aerosol measurements (Fowler et al., 1998), or atmospheric transport models (e.g., RGAR, 1997), suggest an export of around 150 kt NH }N yr~1. This indicated a gap in the UK x ammonia budget of around 90 kt NH }N yr~1. x The revised estimates of non-agricultural NH emis3 sions estimated here help reduce this gap, but do not eliminate it completely. Combining current estimated agricultural NH emissions of 229 kt NH }N yr~1 3 3 (Pain, pers. comm., 1998), with the non-agricultural emissions of 54 kt yr~1, provides a total emission of 283 kt NH }N yr~1. If the same deposition and import "gures 3 are applied, this allows a net export of 83 kt NH }N yr~1, representing a shortfall in the budget of x 67 kt yr~1. Despite the uncertainties inherent in using the same deposition estimates above for 1996, it is clear that the budget is still not completely closed, with the estimated export (83 kt yr~1) approximately half the amount expected (150 kt yr~1). As NH emissions begin to come under the spotlight 3 of international pollution abatement policies (e.g., Bull and Sutton, 1998), these uncertainties become highly relevant in establishing whether planned emission and deposition reductions can be achieved. Further work on the components of the NH budget is therefore clearly x required, both to identify best estimates correctly and reduce uncertainties. At present, the lack of closure in the budget may be accounted for by the upper uncertainty limit of the non-agricultural sources, and is very easily explained if the uncertainties in the agricultural emissions and total deposition are included.

Acknowledgements We are grateful for the funding of this review from the UK Ministry of Agriculture Fisheries and Foods (WA0649), together with the funding of the underlying studies on NH at ITE by the UK Department of En3 vironment, Transport and the Regions, MAFF, the European Commission (DGXII) and the UK NERC. Colleagues at ITE, IGER, ADAS and two anonymous referees provided helpful comments on an earlier draft of this paper.

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