Measurements of nitrogen dioxide in Greenland using Palmes diffusion tubes

Efficacy of passive sampler collection for atmospheric NO2 isotopes under simulated environmental conditions

RATIONALE

Nitrogen oxides or NO_x (NO_x = NO + NO₂ ) play an important role in air quality, atmospheric chemistry, and climate. The isotopic compositions of anthropogenic and natural NO₂ sources are wide-ranging, and they can be used to constrain sources of ambient NO₂ and associated atmospheric deposition of nitrogen compounds. While passive sample collection of NO₂ isotopes has been used in field studies to determine NO_x source influences on atmospheric deposition, this approach has not been evaluated for accuracy or precision under different environmental conditions.

METHODS

The efficacy of NO₂ passive sampler collection for NO₂ isotopes was evaluated under varied temperature and relative humidity (RH) conditions in a dynamic flux chamber. The precision and accuracy of the filter NO₂ collection as nitrite (NO₂^- ) for isotopic analysis were determined using a reference NO₂ gas tank and through inter-calibration with a modified EPA Method 7. The bacterial denitrifer method was used to convert 20 μM of collected NO₂^- or nitrate (NO₃^- ) into N₂ O and was carried out on an Isoprime continuous flow isotope ratio mass spectrometer.

RESULTS

δ¹⁵ N-NO₂ values determined from passive NO₂ collection, in conditions of 11-34 °C, 1-78% RH, have an overall accuracy and precision of ±2.1 ‰, and individual run precision of ±0.6 ‰. δ¹⁸ O-NO₂ values obtained from passive NO₂ sampler collection, under the same conditions, have an overall precision of ± 1.3 ‰.

CONCLUSIONS

Suitable conditions for passive sampler collection of NO₂ isotopes are in environments ranging from 11 to 34 °C and 1 to 78% RH. The passive NO₂ isotope measurement technique provides an accurate method to determine variations in atmospheric δ¹⁵ N-NO₂ values and a precise method for determining atmospheric δ¹⁸ O-NO₂ values. The ability to measure NO₂ isotopes over spatial gradients at the same temporal resolution provides a unique perspective on the extent and seasonality of fluctuations in atmospheric NO₂ isotopic compositions. Copyright © 2017 John Wiley & Sons, Ltd.

Spatial and temporal analysis of ground level ozone and nitrogen dioxide concentration across the twin cities of Pakistan

The analyses presented in this paper include the concentration levels of NO2 and O3 measured during 2 successive years in twin cities (Rawalpindi and Islamabad) of Pakistan from November 2009 to March 2011. NO2 was determined using the passive sampling method, while ozone was determined by Model 400E ozone analyzer. The average NO2 and O3 concentration in twin cities of Pakistan was found to be 44 ± 6 and 18.2 ± 1.24 ppb, respectively. Results indicate that the concentration of NO2 and O3 show seasonal variations. Results also depict that NO2 and O3 concentration levels are high in areas of intense traffic flow and congestion. Rawalpindi has more elevated levels of NO2 and O3 as compared to the Islamabad due to the narrow roads, enclosing architecture of road network and congestion. Climatic variables also influenced the NO2 and O3 concentration, i.e., temperature is positively related with O3, while negatively related with NO2, relative humidity is directly related with NO2 and inversely related with O3, whereas rainfall show negative association with both NO2 and O3 concentration. Comparing the results with WHO standards reveals that NO2 concentration levels at all the sampling points are above the permissible limit, while ozone concentration is still lower than the WHO standards. Thus, there is a need to take appropriate steps to control these continuously increasing levels of NO2 and O3 before they become a serious hazard for the environment and people living in those areas.

A second look at the Palmes' diffusive sampler

The Palmes' tube, the first diffusive sampler incorporating a fixed path length, has received wide usage for the sampling of a large number of gaseous pollutants. But despite numerous previous studies, questions remain regarding the accuracy of these inexpensive, simple-to-construct, open-ended samplers. Here the mass transfer resistance in a Palmes' diffusive sampler was measured using the loss of cyclohexane from a Palmes' tube containing liquid cyclohexane at its base. The average loss rates, at factorial combinations of five air incidence angles evenly spaced from 270 degrees to 90 degrees, and five air speeds from 0.5 m/sec to 2.5 m/sec ranged from 46% to 121% higher than rates calculated from the physical dimensions of the sampler, proving the need to calibrate these samplers rather than relying on a theoretical calculation. The mass transfer resistance was nearly constant when the airflow was perpendicular to the sampler and sufficiently high to avoid stagnation, a finding that may explain the widespread acceptance of the results obtained using this sampler.

Allergen sensitization and allergen exposure in Greenlander Inuit residing in Denmark and Greenland

The aim of this study was to estimate the prevalence of allergic sensitization and possible risk factors in a genetically homogenous Inuit population living under widely differing climatic and cultural conditions. A written questionnaire and skin prick test for 10 aeroallergens were obtained from 1119 adult Greenlanders residing in Denmark, Nuuk (main city in Southern Greenland) and Uummannaq (rural settlement in Northern Greenland). Allergen exposure was assessed by pollen counts, questions on pet keeping and counts of house dust mites in dust samples. The overall prevalence of at least one positive skin prick test was 22.8% in Denmark, 10.6% in Nuuk, and 6.4% in Uummannaq. In Denmark, the total birch pollen counts were 40-1000 times higher compared to Nuuk, whereas the grass pollen count was 13-30 times higher in Denmark compared to Nuuk. Dogs were held indoor with a similar frequency in Denmark and Nuuk, but much less frequently in Uummannaq. In Denmark, house dust mites were found in 72% of house holds (>10/0.1 g dust). Less than 15% of households in Greenland had measurable levels of house dust mites. The prevalence of sensitization to aeroallergens in Inuit Greenlanders differed significantly between Denmark, Nuuk and Uummannaq. These findings correlated with the observed differences in population allergen exposure in the three regions. Furthermore, differences in lifestyle factors such as educational level, stress and ethnic self-identification seemed to be associated with the risk of allergic sensitization in Greenland.