Intercomparison of Clean Air Status and Trends Network Nitrate and Nitric Acid Measurements with Data from Other Monitoring Programs

Abstract

The U.S. Environmental Protection Agency Clean Air Status and Trends Network (CASTNET) utilizes an open-face filter pack system to measure concentrations of atmospheric sulfur and nitrogen species. Concentration data for nitrogen species measured with filter pack systems sometimes deviate from data collected by other measurement systems used to measure the same species. The nature of these differences suggests that more than one sampling mechanism or atmospheric process is involved. The study presented here examines these differences by intercomparing CASTNET data with data from other studies, examining the results from earlier intercomparison studies, and conducting a field test to investigate the effect of particle size on filter pack measurement systems. Measurements of nitrogen species from the Maryland Aerosol Research and Characterization (MARCH) monitoring site were compared with nitrogen concentrations at three nearby CASTNET sites. Results indicate that CASTNET measured higher particulate nitrate (NO) and lower gaseous nitric acid (HNO) concentrations. Comparisons of NO from 34 collocated CASTNET and Inter-agency Monitoring of Protected Visual Environments (IMPROVE) sites show that CASTNET NO measurements were typically higher than the corresponding IM PROVE values. Also, results from the Lake Michigan Air Director's Consortium Midwest Ammonia Monitoring Project demonstrated NO dissociation on Teflon filters. To investigate the effect of particle size, filter pack measurement systems were operated at three CASTNET sites with and without cyclones during six 7-day measurement periods from March to August 2006. Results indicate the size-selection cyclones had a significant effect on both NO and HNO concentrations, but little effect on sulfate (SO) and ammonium (NH) levels. NO concentrations sampled with the open-face filters were significantly higher than concentrations measured with a 2.5-μm cut point, as were HNO concentrations. Although limited in spatial and temporal coverage, the field study showed that the use of an open-face filter pack may allow for the collection of coarse NO particles and for the reaction of HNO with metals/salts on the Teflon filter.

Seasonal composition of remote and urban fine particulate matter in the United States

“…CASTNET collects weekly integrated open‐air samples for the analysis of atmospheric sulfur and nitrogen species. Comparisons of IMPROVE and CASTNET data at collocated sites have been the focus of several studies [e.g., Ames and Malm , 2001; Malm et al , 2002; Sickels and Shadwick , 2008; Lavery et al , 2009] and generally suggest good agreement for sulfate ion concentrations, less so for nitrate ion concentrations [ Lavery et al , 2009]. Using weekly precipitation samples collected by the NADP, Lehmann and Gay [2011] report spatial and temporal trends for sulfate and nitrate concentrations in precipitation that suggest similar spatial patterns to particulate concentrations in the atmosphere.…”

Concentrations and radiative forcing of anthropogenic aerosols from 1750 to 2014 simulated with the Oslo CTM3 and CEDS emission inventory

“…Multi-model studies have shown variations in global BC burden and lifetime of up to a factor of 4-5 (Lee et al, 2013;Samset et al, 2014). Previous comparisons of modeled BC distributions with observations have also pointed to two distinct features common to many models: an overestimation of high-altitude concentrations at low latitudes to midlatitudes and discrepancies in the magnitude and seasonal cycle of high-latitude surface concentrations (e.g., Eckhardt et al, 2015;Lee et al, 2013;Samset et al, 2014;. As accurate representation of the observed aerosol distributions in global models is crucial for confidence in estimates of RF, these issues emphasize the need for broad and up-to-date evaluation of model performance.…”

Interferences with aerosol acidity quantification due to gas-phase ammonia uptake onto acidic sulfate filter samples

“…CASTNET uses an open-face system to collect aerosols on Teflon filters for approximately 1 week for each filter (Lavery et al, 2009). In comparison, the Chemical Speciation Monitoring Network (CSN), which also samples the continental United States and collects the aerosols on nylon or Teflon filters, a denuder is used to scrub gas-phase ammonia to minimize interaction of ammonia with acidic aerosols on filters (Solomon et al, 2000(Solomon et al, , 2014.…”