Estimation of NO<sub>x</sub> emissions from Delhi using Car MAX-DOAS observations and comparison with OMI satellite data

Abstract

Abstract. We present the first Multi-Axis-(MAX-) DOAS observations in India performed during April 2010 and January 2011 in Delhi and nearby regions. The MAX-DOAS instrument was mounted on a car roof, which allowed us to perform measurements along individual driving routes. From car MAX-DOAS observations along closed circles around Delhi, together with information on wind speed and direction, the NO x emissions from the greater Delhi area were determined: our estimate of 4.4 × 10 25 molecules s −1 is found to be slightly lower than the corresponding emission estimates using the EDGAR emission inventory and substantially smaller compared to a recent study by Gurjar et al. (2004). We also determined NO x emissions from Delhi using OMI satellite observations on the same days. These emissions are slightly smaller than those from the car MAX-DOAS measurements. Finally the car MAX-DOAS observations were also used for the validation of simultaneous OMI satellite measurements of the tropospheric NO 2 VCD and found a good agreement of the spatial patterns. Concerning the absolute values, OMI data are, on average, higher than the car MAX-DOAS observations close to strong emission sources, and vice versa over less polluted regions. Our results indicate that OMI NO 2 VCDs are biased low over strongly polluted regions, probably caused by inadequate apriori profiles used in the OMI satellite retrieval.

High-resolution airborne imaging DOAS measurements of NO<sub>2</sub> above Bucharest during AROMAT

“…More detailed information about the MPIC and UGAL VCD retrieval algorithms used can be found in Wagner et al (2010) and Shaiganfar et al (2011) as well as Constantin et al (2013), respectively.…”

“…10 Estimation of the urban NO x emission rate Several studies have investigated the NO x emission rate of point sources and urban areas Shaiganfar et al, 2011;Beirle et al, 2011;Liu et al, 2016). Here we adapt the method presented in Ibrahim et al (2010) and Shaiganfar et al (2011), where urban emissions are estimated from an encircled area, by integrating along the route of a circle S. This method is based on Gauss's divergence theorem, describing the relation between the flux of a vector field through a closed surface (measured) and the divergence of the vector field inside the enclosed volume (emissions inside that volume).…”

“…Here we adapt the method presented in Ibrahim et al (2010) and Shaiganfar et al (2011), where urban emissions are estimated from an encircled area, by integrating along the route of a circle S. This method is based on Gauss's divergence theorem, describing the relation between the flux of a vector field through a closed surface (measured) and the divergence of the vector field inside the enclosed volume (emissions inside that volume). The NO 2 emission rate F NO 2 may be estimated from…”

Development of a digital mobile solar tracker

“…Spectra collected from different EAs contain information from different layers in the atmosphere and hence can be used to obtain information about the vertical distribution of the trace gases. However, due to the horizontal gradient of the trace gases of interest, MAX-DOAS measurements from a mobile platform are focused on obtaining VCDs using one or two EAs (e.g., Ibrahim et al, 2010;Shaiganfar et al, 2011;Wang et al, 2012). During FRAPPE 2014, the MAX-DOAS instrument made measurements at 30 • (facing backward relative to the mobile platform) and 90 • (zenith) EAs.…”

“…Combined with wind measurements, mobile column measurements of trace gases have been shown to be very useful to constrain emission of trace gases from source regions by applying a mass conservation approach (e.g., Baidar et al, 2013b;Ibrahim et al, 2010;Johansson et al, 2014a, b;Mellqvist et al, 2010;Shaiganfar et al, 2011;Wang et al, 2012). Mobile column measurements from various platforms have previously been used to estimate nitrogen oxides (NO x ) emissions from cities (Baidar et al, 2013b;Ibrahim et al, 2010;Shaiganfar et al, 2011;Wang et al, 2012), nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ) (Johansson et al, 2014a), and formaldehyde (HCHO) (Johansson et al, 2014b) from industries using the differential optical absorption spectroscopy (DOAS) (Platt and Stutz, 2008) technique and fugitive volatile organic compound (VOC) emissions from refineries (e.g., Mellqvist et al, 2010;Johansson et al, 2014a, b) using the solar occultation flux (SOF) (Mellqvist et al, 2010) method. The DOAS method typically is limited to the UV-Vis wavelength region and uses scattered sunlight; while the SOF method uses direct sun observations in the mid-IR wavelengths.…”