A continuous-flow denuder for the measurement of ambient concentrations and surface-exchange fluxes of ammonia

doi:10.1016/0960-1686(93)90280-C

Atmospheric Environment. Part A. General Topics

Volume 27, Issue 13, September 1993, Pages 2085-2090

https://doi.org/10.1016/0960-1686(93)90280-C Get rights and content

Abstract

A new diffusion denuder is described for the continuous measurement of atmospheric ammonia. Ammonia is collected in an absorption solution in a rotating denuder, separated from interfering compounds by diffusion through a semi-permeable membrane and detected by conductometry. The method is free from interferences by other atmospheric gases, with the exception of volatile amines. The detection limit is 6 ng m⁻³ for a 30-min integration time. This compact instrument is fully automated and suited for routine deployment in field studies. The precision is sufficiently high for micrometeorological studies of air-surface exchange of ammonia.

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Ammonia (NH₃) plays a significant role in the formation of atmospheric particulate matter, and influences on environmental and public health as well as climate change. Thus, it is important to sensitive measurement of atmospheric NH₃. In the present work, a sub-ppb level standoff open-path NH₃ sensor was developed for on line, sensitive measurement of atmospheric NH₃. A 9.06 μm distributed feedback quantum cascade laser was employed to probe the ammonia absorption lines located on fundamental rotational-vibrational absorption band and calibration-free wavelength modulation spectroscopy technique was employed to retrieve NH₃ concentration directly. The standoff open-path NH₃ sensor performance was investigated in laboratory corridor with 80 m open path length (Hefei, China) and a minimum detection limit of 0.46 ppb (3σ) was obtained. Finally, field campaign measurement was carried out in a winter wheat farmland (Changshu, China). Field measurement shown that the concentration of NH₃ varies from 7 ppb to 30 ppb with an average of 14 ppb. The developed standoff sensor has high potential to be a robust tool for monitoring atmospheric NH₃ or study of regional ammonia emissions in farmland or feedlot scale.
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Particulate matter source apportionment (SA) is the basis and premise for preventing and controlling haze pollution scientifically and effectively. Traditional offline SA methods lack the capability of handling the rapid changing pollution sources during heavy air pollution periods. With the development of multiple online observation techniques, online SA of particulate matter can now be realized with high temporal resolution, stable and reliable continuous observation data on particle compositions. Here, we start with a summary of online measuring instruments for monitoring particulate matters that contains both online mass concentration (online MC) measurement, and online mass spectrometric (online MS) techniques. The former technique collects ambient particulate matter onto filter membrane and measures the concentrations of chemical components in the particulate matter subsequently. The latter technique could be further divided into two categories: bulk measurement and single particle measurement. Aerosol Mass Spectrometers (AMS) could provide mass spectral information of chemical components of non-refractory aerosols, especially organic aerosols. While the emergence of single-particle aerosol mass spectrometer (SPAMS) technology can provide large number of high time resolution data for online source resolution. This is closely followed by an overview of the methods and results of SA. However, online instruments are still facing challenges, such as abnormal or missing measurements, that could impact the accuracy of online dataset. Machine leaning algorithm are suited for processing the large amount of online observation data, which could be further considered. In addition, the key research challenges and future directions are presented including the integration of online dataset from different online instruments, the ensemble-trained source apportionment approach, and the quantification of source-category-specific human health risk based on online instrumentation and SA methods.
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Water soluble inorganic chemical ions of PM₁ and PM_2.5 and atmospheric trace gases were monitored simultaneously on hourly resolution at Indira Gandhi International Airport (IGIA), Delhi during 8 December 2017–10 February 2018. Monitoring was made by MARGA (Monitoring AeRosol and Gases in ambient Air) under winter fog experiment (WIFEX) program of the Ministry of Earth Sciences (MoES), Government of India. The result based on the analysis of the data so generated reveals that Cl⁻, NH₄⁺, NO₃⁻ and SO₄²⁻ were dominant ions in order which collectively constituted 96.8 and 97.3% of the of the total measured ionic mass in PM₁ and PM_2.5 respectively. Their overall average concentrations in PM₁ were 19.5 ± 19.7, 18.4 ± 10.5, 16.6 ± 8.7 and 10.3 ± 5.7 μg/m³ and in PM_2.5 were 36.0 ± 33.9, 32.7 ± 17.2, 28.5 ± 13.6 and 19.9 ± 13.9 μg/m³. Average concentrations of HCl, HNO₃, HNO₂, SO₂ and NH₃ trace gases were 0.7 ± 0.3, 2.7 ± 1.1, 6.6 ± 4.7, 22.0 ± 12.3 and 25.7 ± 9.1 μg/m³ respectively. Weather parameters along with low mixing height played significant role in the occurrence of high concentration of these chemical species.
NH₄⁺ was the prime neutralizer of the acidic components and mostly occurred in (NH₄)₂SO₄/NH₄HSO₄, NH₄NO₃ and NH₄Cl molecular forms. Major sources of these chemical species were fossil fuel combustion in aviation activity and transportation, coal burning in thermal power plants, industrial processes and emissions from biomass burning and agro-based activity.
The quality of air with respect to PM_2.5 always remained deteriorated. It became alarming during low visibility period mainly due to high concentration of Cl⁻, NO₃⁻, SO₄²⁻ and NH₄⁺. Both meteorological and chemical processes interactively fed each other which occasionally resulted in fog development and visibility degradation. The knowledge gained by this study will help in simulation of atmospheric processes which lead to fog development and dispersal in the Delhi region.

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Technical noteA continuous-flow denuder for the measurement of ambient concentrations and surface-exchange fluxes of ammonia

Abstract

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Atmospheric Environment

Tungstic acid for preconcentration and determination of gaseous and particulate ammonia and nitric acid in ambient air

Analyt. Chem.

Automated measurement of atmospheric trace gases. Diffusion-based collection and analysis

Technical note
A continuous-flow denuder for the measurement of ambient concentrations and surface-exchange fluxes of ammonia