Correlating the Spatial Distribution of Atmospheric Ammonia with ?15N Values at an Ammonia Release Site

Nitrogen isotope variations of ammonium across rain events: Implications for different scavenging between ammonia and particulate ammonium

Enhanced ammonia (NH₃) emissions and deposition caused negative effects on air quality and ecosystems. Precipitation is an efficient pathway to remove NH₃ and particulate ammonium (p-NH₄⁺) from the atmosphere into ecosystems. However, precipitation scavenging of p-NH₄⁺ in chemical transport models has often considered fine p-NH₄⁺, with inadequate constraints on NH₃ and coarse p-NH₄⁺. Based on distinct δ¹⁵N values between NH₃ and NH₄⁺ in PM_2.5 (particulate matters with aerodynamic diameters ≤ 2.5 μm) or TSP (total suspended particulates), this paper interpreted intra-event variations of precipitation NH₄⁺ concentrations and δ¹⁵N values (δ¹⁵N-NH₄⁺ values) at Guiyang (Xiao et al., 2015). Generally decreased NH₄⁺ concentrations across rain events reflected decreasing scavenging of NH₃ and p-NH₄⁺. Using a Bayesian isotope mixing model, we found that differing contributions between ¹⁵N-depleted NH₃ and ¹⁵N-enriched p-NH₄⁺ were responsible for the three-stage variations of intra-event δ¹⁵N-NH₄⁺ values. The decreases of δ¹⁵N-NH₄⁺ values across the first and third stages indicated more decreases in scavenging p-NH₄⁺ than NH₃, while the increases of δ¹⁵N-NH₄⁺ values across the second stage were resulted primarily from more increases in scavenging p-NH₄⁺ (particularly fine p-NH₄⁺) than NH₃. These results stressed influences of differing scavenging between NH₃ and p-NH₄⁺ on precipitation δ¹⁵N-NH₄⁺ values, which should be considered in modeling precipitation scavenging of atmospheric p-NH₄⁺.

Lichens as a useful mapping tool?--an approach to assess atmospheric N loads in Germany by total N content and stable isotope signature

To assess whether nitrogen (N) content and δ(15)N ratios in nitrophytic lichen species (Xanthoria parietina (L.) Th. Fr. (1860) and Physcia spp. (Schreb.) Michaux (1803)) reflect the quantity and quality of atmospheric N loads, 348 lichen samples from 174 sampling grid cells were investigated in the western part of Germany. The analysed lichen N content ranged between 0.98 and 4.28 % and δ(15)N ratios between -15.2 and -1.3 ‰. Based on the N concentrations and the δ(15)N ratios of lichens, different landscape categories and coupled N deposition rates could be inferred for different regions of Germany. By analysing environmental variables like altitude, ammonia emission density, livestock unit and different defined deposition types, a direct relationship was found between lichen chemistry and N compounds produced from agricultural activity. The results support the development of a monitoring method which could be used nationally or even internationally to support current N deposition measurements, by providing reliable information on the quantity and quality of N deposition in high N environments.

Comparative use of lichens, mosses and tree bark to evaluate nitrogen deposition in Germany

To compare three biomonitoring techniques for assessing nitrogen (N) pollution in Germany, 326 lichen, 153 moss and 187 bark samples were collected from 16 sites of the national N deposition monitoring network. The analysed ranges of N content of all investigated biomonitors (0.32%-4.69%) and the detected δ(15)N values (-15.2‰-1.5‰), made it possible to reveal species specific spatial patterns of N concentrations in biota to indicate atmospheric N deposition in Germany. The comparison with measured and modelled N deposition data shows that particularly lichens are able to reflect the local N deposition originating from agriculture.

Characterizing the isotopic composition of atmospheric ammonia emission sources using passive samplers and a combined oxidation-bacterial denitrifier approach

RATIONALE

Ammonia (NH3) emissions are a substantial source of nitrogen pollution to sensitive terrestrial, aquatic, and marine ecosystems and dependable quantification of NH3 sources is of growing importance due to recently observed increases in ammonium (NH4(+)) deposition rates. While determination of the nitrogen isotopic composition of NH3 (δ(15)N-NH3) can aid in the quantification of NH3 emission sources, existing methods have precluded a comprehensive assessment of δ(15)N-NH3 values from major emission sources.

METHODS

We report an approach for the δ(15)N-NH4(+) analysis of low concentration NH4(+) samples that couples the bromate oxidation of NH4(+) to NO2(-) and the microbial denitrifier method for δ(15)N-NO2(-) analysis. This approach reduces the required sample mass by 50-fold relative to standard elemental analysis (EA) procedures, is capable of high throughput, and eliminates toxic chemicals used in a prior method for the analysis of low concentration samples. Using this approach, we report a comprehensive inventory of δ(15)N-NH3 values from major emission sources (including livestock operations, marine sources, vehicles, fertilized cornfields) collected using passive sampling devices.

RESULTS

The δ(15)N-NH4(+) analysis approach developed has a standard deviation of ±0.7‰ and was used to analyze passively collected NH3 emissions with a wide range of ambient NH3 concentrations (0.2 to 165.6 µg/m(3)). The δ(15)N-NH3 values reveal that the NH3 emitted from volatilized livestock waste and fertilizer has relatively low δ(15)N values (-56 to -23‰), allowing it to be differentiated from NH3 emitted from fossil fuel sources that are characterized by relatively high δ(15)N values (-15 to +2‰).

CONCLUSIONS

The isotopic source signatures presented in this emission inventory can be used as an additional tool in identifying NH3 emission sources and tracing their transport across localized landscapes and regions. The insight into the transport of NH3 emissions provided by isotopic investigation is an important step in devising strategies to reduce future NH3 emissions, a mounting concern for air quality scientists, epidemiologists, and policy-makers.

Atmospheric transport of urban-derived NH(x): Evidence from nitrogen concentration and delta(15)N in epilithic mosses at Guiyang, SW China

Nitrogen concentration and delta15N in 175 epilithic moss samples were investigated along four directions from urban to rural sites in Guiyang, SW China. The spatial variations of moss N concentration and delta15N revealed that atmospheric N deposition is dominated by NHx-N from two major sources (urban sewage NH3 and agricultural NH3), the deposition of urban-derived NHx followed a point source pattern characterized by an exponential decline with distance from the urban center, while the agricultural-derived NHx was shown to be a non-point source. The relationship between moss N concentration and distance (y=1.5e(-0.13x)+1.26) indicated that the maximum transporting distance of urban-derived NHx averaged 41 km from the urban center, and it could be determined from the relationship between moss delta(15)N and distance [y=2.54ln(x)-12.227] that urban-derived NHx was proportionally lower than agricultural-derived NHx in N deposition at sites beyond 17.2 km from the urban center. Consequently, the variation of urban-derived NHx with distance from the urban center could be modeled as y=56.272e(-0.116x)-0.481 in the Guiyang area.