DEPOSITION AND ATMOSPHERIC NITROGEN CONCENTRATIONSTRENDS IN CUBA

OSVALDO A. CUESTA SANTOS, PAULO L. ORTIZ BULTO andMARIA L. GONZALEZ GONZALEZ

Meteorological Institute of Cuban Ministry of Science, Technology and Environment, Aptdo 17032,Habana 17, C. P. 11700, Havana City, Cuba

(Received 26 June, 1996; accepted 25 April, 1997)

Abstract. The NO2, nitrate and ammonia sampling in aerosols and rainfall was carried out at fivestations located along the Cuban Island from 1986 to 1991. The sampling and chemical analysis weremade mainly on the basis of methodologies recommended by WMO for above mentioned compoundsat regional level. The total deposition of these compounds varies from 0.706 to 3.317 g m�2 yr�1.The wet deposition is about of 60%, so that the dry one is 40%. The amount of both depositionsdepends on our tropical rainy climate features. For some of these compounds the trend is increasing.

Key words: NO2, nitrate, ammonium

1. Introduction

Daily, new proofs appear that demonstrate that the acid deposition causes problemson enviroment. For that, the harmfulness of acid deposition origined by nitrogen’soxidized compounds (NOx, HNO3 and NO�3 ) is more and more evident in terres-trial and aquatic ecosystems. In addition, the hydrogen ions replace metallic onesnecessary to nutrition and metabolism of plants. Thus, due to its intensity the aciddeposition can potentially break off the mineral cycle on which the agricultural andforest yield depends. Acid deposition can lead to appearance of necrotic spots inthe leaves and foliage and affects its growth and photosynthetical activity (Cuesta,1993).

The acid deposition accelerates the corrosion in most of materials used forbuildings (UNESCO, 1985; Graedel and McGill, 1986; Cuesta, 1992) and canseriously damage the ancient monuments, historical buildings such as sculpturesand cultural objects (Rodhe and Herrera, 1988; Cuestaet al., 1993).

In mid latitude regions where the anthropogenic emission covers the cycles ofsubstances such as nitrogen and sulphur, the wet and dry deposition is of comparableimportance. Near sources where the pollutants’ concentration if high, the drydeposition is relatively more important, but the wet one is being progressively ofgreat importance on moving off the source (W.M.O., 1982).

In the current paper, the deposition of atmospheric nitrogen compounds as NO2

and nitrate and ammonium in aerosols and rainfall and the trend of its concentrationsis discussed for the period of 1986 to 1991 at several stations along the Island ofCuba.

Water, Air, and Soil Pollution106: 163–169, 1998.c 1998Kluwer Academic Publishers. Printed in the Netherlands.

164 OSVALDO A. CUESTA SANTOS ET AL.

Table ICharacteristics of main air pollution control stations network for the nitrogencompounds

Name Latitude Longitude Height Classif. ShoreN W (m) distance km

La Palma 22� 460

83 � 330

47.4 Rural 6.0

Casablanca 23� 100

82 � 210

50.1 Shore with 1.5urban inf.

Colon 22� 410

80 � 450

35.0 Rural 42.0

Falla 22� 060

78 � 370

15.8 Rural 15.0

Stgo Cuba 20� 030

75 � 490

38.0 Urban 8.0residencial

2. Materials and Methods

For preparing the current paper the data from air population control stations’network of Meteorological Institute of Cuban Ministry of Sciency, Technologyand Environment were used. The work of this network (Table I) is conducted bymethodologies recommended by WMO for monitoring and chemically analyzingof above mentioned compounds at regional level. Among the studied stations, threeones present rural characteristics such as La Palma, Colon and Falla and two othershave some urban influence, such as Casablanca and Santiago de Cuba.

For the calculation of wet and dry deposition flows of atmospheric nitrogen, theconcentrations expressed in�g/m3 for NO2, NO�3 and NH+4 were converted intoN (Nitrogen). Concentrations in rainfall are expressed in mg/l.

For dry deposition flows, because of known deficiencies of existing monitoringmethods, its calculations are obtained through the deposition velocity (Garland,1979; Meszaros, 1981; W.M.O., 1991a) and the obtained concentrations frommonitoring. For wet deposition flows the mean weighted concentrations for eachyear (starting from summary monthly samples) and the rainfall quantity were used.The deposition flows are expressed in g m�2 yr�1.

For the concentration trend behaviour two statistic techniques were used. One ofthem is aimed at trend’s detection and another one at its modelling. Both techniquesare based on the Kendall-Man test, which allows the short term persistence, tobe determined, as well as to undertake the retrogressive analysis for definingwhen the change of trend began. The Kendall-Man test consists in the progressivedetermination of the test’s statistics (W.M.O., 1990). For the atmospheric nitrogencompounds a significant trend has been found, the trend’s equation was obtainedfrom the simple regression analysis. All methods were performed in SPSS plusstatistic system.

DEPOSITION AND ATMOSPHERIC NITROGEN CONCENTRATIONS TRENDS IN CUBA165

Figure 1. Total deposition (dry and wet) of the main compounds of nitrogen.

Another aspect studied was the concentrations’ trend during these years. Thisgives information on the behaviour of both natural and anthropogenic sources ofabove mentioned elements.

3. Results and Discussion

The total deposition (dry and wet) for main nitrogen compounds at several stations isreflected in Figure 1. The values expressed in g m�2 yr�1 show that the Casablancaand Santiago de Cuba stations present higher values mainly at Casablanca wherethese values are similar to reported in most of Europe (U.N., 1991). Only in thelarge urban and industrialized centers, the deposition in Europe is significantlyhigher.

The values at studied stations vary from minimum of 0.706 g m�2 yr�1 recordedin Santiago de Cuba city in 1989 (very dry year for eastern region) to maximumof 3.317 g m�2 yr�1 in the same year in Casablanca town where the nitrate andammonium concentrations in the rainfall were considerably highest. This maximumcoincides with the growing of the cuban economy up to 1989, as well as with theincreasing generation of pollutants caused by the industry and transportation. Inaddition to this, approximately 50% of the nitrogen emitted to atmosphere aredeposited on Earth’s surface by rain (W.M.O., 1991b). For instance, the relativeimportance of dry and wet deposition of nitrogen and sulphur’s compoundsdependson many factors such as the climate and surface features in tropical wet areas, where

166 OSVALDO A. CUESTA SANTOS ET AL.

Figure 2. Total deposition for compounds expressed in nitrogen.

the intense rains are of high frequency. Thus, the wet deposition is relatively moreimportant than the dry one (Garland, 1979).

In Cuba, as found in the studied stations’ data, the nitrogen wet depositionrepresents approximately 60%. For our region therefore the wet deposition is con-sidered significant and also depends on characteristics of our tropical rainy climate.The largest air-sea flow of oxidized nitrogen occurs in the North Atlantic Ocean,Europe and Africa (W.M.O., 1991c). The reduced nitrogen forms, mainly NH+

4and NH3, contribute about 40% of N total flow into oceans from the atmosphere(Galbally and Johansson, 1989).

The values attained for Cuba referring to the main kinds of oxidized nitrogenshow that it represents on average 40%, being higher at those stations with higheranthropogenic influence (Casablanca and Santiago de Cuba).

The La Palma station (rural) receives the highest contribution of nitrate viarain; indicating the possibility of transfer from continental sources through kindsof nitrogen that serve as its reservoirs.

The stations of Colon and Falla recieve the lowest amount of oxidized nitrogenbecause of highest power of natural reduced nitrogen kinds’ sources. Figure 2also shows the contribution of each nitrogen compound in g m�2 yr�1 at studiedstations.

DEPOSITION AND ATMOSPHERIC NITROGEN CONCENTRATIONS TRENDS IN CUBA167

Table IITrend equation fit for nitrogen atmospheric compounds

Station Element – Equation

La Palma NO2 = – 0.02559t + 2.352598NH+

4 (a) = 0.015722t + 0.407002NO+

3 (p) = – 0.012721t + 1.254504Stgo de Cuba NO2 = – 0.027176t + 3.595139Colon NO2 = 0.010345t + 1.124493

NH+4 (a) = 0.057033t + 3.568086

Note: Concentrations –�g/m3 t – years

Table IIIDirection of the trend for nitrogen atmospheric compounds

Stations NO2 NO+3 (a) NH+

4 (a) NH+3 (p) NH+

4 (p)

La Palma – + + – +Casablanca – + + – –Stgo de Cuba – – + – –Colon + � + + –Falla + � + + +

Note: (–) direction to decrease, (+) to increase, (�) not data

Tables II and III show the compounds’ equations with a significant trend and itsdirection in atmospheric nitrogen compounds. As it can be seen for NO2, the mon-itoring stations with highest anthropogenic influence as Casablanca and Santiagode Cuba ones have experienced a trend to concentrations’ decrease because of theslowing down of the industrial production and transportation means in Cuba since1989.

This influence seems to also affect the La Palma station which among ruralstations receives the highest oxidated compounds’ deposition.

On the other hand, the Colon rural station presents a significant trend to NO2

concentration increase (Figure 3), as well as the Falla station also experiencesincreases. These two rural stations seem to be influenced by the biomass burningfor energy purposes.

The nitrate’s particles experience a trend to increase in La Palma and Casablancastations. This has been caused by possible long range transport (Cuesta, 1993) ofsubstances which serve as reservoirs of NOx.

In addition, the direction of increasing trends in ammonium aerosol amountbecomes interesting in all studied sites, because it reaches a significant trend toincrease in La Palma and Colon rural stations, mainly caused by ammoniac use asfertilizer over these areas.

168 OSVALDO A. CUESTA SANTOS ET AL.

Figure 3. The NO2 concentrations trend.

Relating to the rainfall, the nitrate has as a similar behaviour as NO2 in thesestations, but only in the La Palma station does the nitrate experience a significanttrend to increase in concentrations, while the ammonium in the rainfall tends onlyto increase in La Palma and Falla stations, both considered as rural. In general, thetrend of each of analyzed elements depends on characteristics and intensities of thesources.

4. Conclusions

In Cuba, the total deposition for main nitrogen compounds varies from 0.706 to3.317 g m�2 yr�1. The wet deposition is about 60%, and the dry one is 40%.The oxidized nitrogen compounds contribute 40% and the reduced ones 60%,in accordance with natural sources potential depending in Cuba’s tropical rainyclimate.

In the stations with an urban influence, the NO2 trend is similar to the nitratetrend in the rainfall. In the Colon and Falla rural stations, the monitoring shallbe permanently undertaken due to the trend to increase in nitrogen’s oxidizedcompounds concentrations, to determine if a future potential danger exists foragricultural regions.

DEPOSITION AND ATMOSPHERIC NITROGEN CONCENTRATIONS TRENDS IN CUBA169

Acknowledgments

Special thanks to Mrs. Ivonne Suarez Rousseaoux, technician, and to Mr. FidelYllarza Rodrıguez (m.A.) for his English version of this manuscript.

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