The Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI): design, execution, and early results

Abstract

From June to July 2009 more than thirty different in-situ and remote sensing instruments from all over the world participated in the Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI). The campaign took place at KNMI's Cabauw Experimental Site for Atmospheric Research in the Netherlands. Its main objectives were to determine the accuracy of state-of-the-art ground-based measurement techniques for the detection of atmospheric nitrogen dioxide (both in-situ and remote sensing), and to investigate their usability in satellite data validation. The expected outcomes are recommendations regarding the operation and calibration of such instruments, retrieval settings, and observation strategies for the use in ground-based networks for air quality monitoring and satellite data validation. Twenty-four optical spectrometers participated in the campaign, of which twenty-one had the capability to scan different elevation angles consecutively, the so-called Multi-axis DOAS systems, thereby collecting vertical profile information, in particular for nitrogen dioxide and aerosol. Various in-situ samplers simultaneously characterized the variability of atmospheric trace gases and the physical properties of aerosol particles. A large data set of continuous measurements of these atmospheric constituents has been collected under various meteorological conditions and air pollution levels. Together with the permanent measurement capability at the Cabauw site characterizing the meteorological state of the atmosphere, the CINDI campaign provided a comprehensive observational data set of atmospheric constituents in a highly polluted region of the world during summertime. First detailed comparisons performed with the CINDI data show that slant column measurements of NO<sub>2</sub>, O<sub>4</sub> and HCHO with MAX-DOAS agree within 5 to 15%, vertical profiles of NO<sub>2</sub> derived from several independent instruments agree within 25%, and MAX-DOAS aerosol optical thickness agrees within 20–30% with AERONET data. For the in-situ NO<sub>2</sub> instrument using a molybdenum converter, a bias was found as large as 5 ppbv during day time, when compared to the other in-situ instruments using photolytic converters

Comparison of Near‐Surface NO2 Pollution With Pandora Total Column NO2 During the Korea‐United States Ocean Color (KORUS OC) Campaign

“…Thus, there is a need for independent verification of the satellite column amount and parallel measurement of surface NO 2 . Among a number of ground‐based spectrometric approaches to TC NO 2 (Piters et al, ; Kreher et al, ) is the Pandora Spectrometer Instrument (PSI). Recently, Herman et al () surveyed OMI TC NO 2 patterns over six multiyear PSI stations in Korea and the U.S.…”

OMI Satellite and Ground‐Based Pandora Observations and Their Application to Surface NO2 Estimations at Terrestrial and Marine Sites

“…These large differences between the ground measurements and Pandora could also be attributed to interference species measured by the gas analyzer using a molybdenum converter. In Piters et al (), a comparison between this type of instrument and a photolytic converter found differences as large as 5 ppbv during the day time. The solar UV needed to generate these interfering species was still present on many of these days where rainfall was not constant the entire day.…”

“…Wang et al () showed that Pandora slant column abundances agree with those obtained from a multifunction differential optical absorption spectroscopy (DOAS) to within 5%. Validation results from the CINDI (Cabauw Intercomparison Campaign for Nitrogen Dioxide Measuring Instruments) campaign have also indicated that MAX‐DOAS slant column densities of NO 2 from multiple instruments, including Pandora, have agreement of approximately 5–10% (Piters et al, ) under clear sky conditions. This measurement site of the CINDI campaign, Cabauw, the Netherlands, is similar to Welgegund in that it does not have major local sources of trace gases like NO 2 but rather is impacted from transported pollution being downwind of urban areas (i.e., Rotterdam, Netherlands).…”

“…NO 2 mixing ratios often display considerable vertical gradients within the PBL (Piters et al, ). The method for estimating surface NO 2 from a column amount developed by Knepp et al () assumes that surface emissions are well‐mixed within the PBL as a first‐order approximation (Leigh et al, ).…”

“…Lamsal et al (, ) showed that ground‐level NO 2 concentrations obtained from OMI simulated with a chemical transport model agree well with corrected in situ measurements in the U.S. and Canada. Similar studies (e.g., Halla et al, ; Lee et al, ; Leigh et al, ; Luo et al, ; Petritoli et al, ; Piters et al, ), comparing satellite or ground‐retrieved columns to surface measurements, have utilized complex chemical transport models and/or large averaging times (weekly, seasonal, or annual) that effectively average out the influence of PBL variability. These methods are often inadequate for interpreting health‐related NO 2 fluctuations that occur on the order of hours.…”