First comparison between ground‐based and satellite‐borne measurements of tropospheric nitrogen dioxide in the Po basin

Abstract

[1] In this paper we present in situ and tropospheric column measurements of NO 2 in the Po river basin (northern Italy). The aim of the work is to provide a quantitative comparison between ground-based and satellite measurements in order to assess the validity of spaceborne measurements for estimating NO 2 emissions and evaluate possible climatic effects. The study is carried out using in situ chemiluminescent instrumentation installed in the Po valley, a UV/Vis spectrometer installed at Mount Cimone (44.2°N, 10.7°E, 2165 m asl), and tropospheric column measurements obtained from the Global Ozone Monitoring Experiment (GOME) spectrometer. Results show that the annual cycle in surface concentrations and also some specific pollution periods observed by the air quality network are well reproduced by the GOME measurements. However, tropospheric columns derived from the surface measurements assuming a well-mixed planetary boundary layer (PBL) are much larger than the GOME columns and also have a different seasonal cycle. This is interpreted as indication of a smaller and less variable mixing height for NO 2 in the boundary layer. Under particular meteorological conditions the agreement between UV/Vis tropospheric column observations and GOME measurements in the Mount Cimone area is good (R 2 = 0.9) with the mixing properties of the atmosphere being the most important parameter for a valid comparison of the measurements. However, even when the atmospheric mixing properties are optimal for comparison, the ratio between GOME and ground-based tropospheric column data may not be unity. It is demonstrated that the values obtained (less than 1) are related to the fraction of the satellite ground pixel occupied by the NO 2 hot spot.

SCIAMACHY tropospheric NO<sub>2</sub> over Switzerland: estimates of NO<sub>x</sub> lifetimes and impact of the complex Alpine topography on the retrieval

“…The normalised seasonal variation of the ground-based data agrees reasonably well with the variation observed by GOME, in particular regarding the large differences between summer and winter. Similarly pronounced seasonal variations of space-borne NO 2 VTCs over industrialised regions have also been reported by Petritoli et al (2004), Richter et al (2005), van der A et al (2006) and Uno et al (2006). The seasonal amplitude in the SCIAMACHY data, however, is lower than in both GOME and ground-based observations: For the median values the amplitude is reduced by more than a factor of two.…”

Ground‐level nitrogen dioxide concentrations inferred from the satellite‐borne Ozone Monitoring Instrument

“…Observations of a weekly pattern in GOME tropospheric NO 2 columns with significant reductions on weekends [Beirle et al, 2003], diurnal variation in NO 2 columns driven by emissions and photochemistry [Boersma et al, 2008a], and a large increase in tropospheric NO 2 columns over eastern China inferred from GOME and SCIAMACHY [Richter et al, 2005;van der A et al, 2006] demonstrate the capability of observing air pollution from space. Petritoli et al [2004] and Ordóñez et al [2006] found a significant correlation between in situ NO 2 measurements and GOME tropospheric NO 2 columns. Airborne measurements in the southeastern United States reveal that NO 2 in the boundary layer can make a dominant contribution to the NO 2 tropospheric column over polluted regions [Martin et al, 2004a;Bucsela et al, 2008].…”

Near-real time retrieval of tropospheric NO<sub>2</sub> from OMI

“…But validation efforts for various retrievals show acceptable accuracy (Heland et al, 2002;Petritoli et al, 2004;Martin et al, 2004Martin et al, , 2006Petritoli et al, 2005;Cede et al, 2006;Ordóñez et al, 2006;Schaub et al, 2006) for GOME and SCIAMACHY NO 2 .…”