Validation of MAX-DOAS retrievals of aerosol extinction, SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, and NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; through comparison with lidar, sun photometer, active DOAS, and aircraft measurements in the Athabasca oil sands region

Zoe Davis ,Sabour Baray,Ihab Abboud,Akshay Lobo,Megan D Willis,Alex K Y Lee,Udo Frieß,Hans D Osthoff,Jeff Brook,Elijah G Schnitzler,Monika Aggarwaal,Chris A Mclinden,K B Strawbridge ,C Mihele ,J A Whiteway ,Vitali Fioletov ,Jason S Olfert ,R M Staebler ,Jason O’brien ,R Mclaren

doi:10.5194/amt-13-1129-2020

Abstract

Abstract. Vertical profiles of aerosols, NO2, and SO2 were retrieved from Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements at a field site in northern Alberta, Canada, during August and September 2013. The site is approximately 16 km north of two mining operations that are major sources of industrial pollution in the Athabasca oil sands region. Pollution conditions during the study ranged from atmospheric background conditions to heavily polluted with elevated plumes, according to the meteorology. This study aimed to evaluate the performance of the aerosol and trace gas retrievals through comparison with data from a suite of other instruments. Comparisons of aerosol optical depths (AODs) from MAX-DOAS aerosol retrievals, lidar vertical profiles of aerosol extinction, and the AERONET sun photometer indicate good performance by the MAX-DOAS retrievals. These comparisons and modelling of the lidar S ratio highlight the need for accurate knowledge of the temporal variation in the S ratio when comparing MAX-DOAS and lidar data. Comparisons of MAX-DOAS NO2 and SO2 retrievals to Pandora spectral sun photometer vertical column densities (VCDs) and active DOAS mixing ratios indicate good performance of the retrievals, except when vertical profiles of pollutants within the boundary layer varied rapidly, temporally, and spatially. Near-surface retrievals tended to overestimate active DOAS mixing ratios. The MAX-DOAS observed elevated pollution plumes not observed by the active DOAS, highlighting one of the instrument's main advantages. Aircraft measurements of SO2 were used to validate retrieved vertical profiles of SO2. Advantages of the MAX-DOAS instrument include increasing sensitivity towards the surface and the ability to simultaneously retrieve vertical profiles of aerosols and trace gases without requiring additional parameters, such as the S ratio. This complex dataset provided a rare opportunity to evaluate the performance of the MAX-DOAS retrievals under varying atmospheric conditions.

Highlights

The Athabasca oil sands operations in Alberta contain significant sources of industrial atmospheric pollutants, such as sulfur dioxide (SO2) and nitrogen dioxide (NO2) (ECCC, 2018b, c)
The lidar measurements indicate that the contribution of the aerosol optical depths (AODs) above 2 km can vary significantly, as indicated by a comparison of aerosol extinction vertical profiles from 4 September and 23 August (Fig. S9). These results indicate that the ratio of the MAX-Differential Optical Absorption Spectroscopy (DOAS) AODs to AERONET AODs depends on the location of the aerosol exwww.atmos-meas-tech.net/13/1129/2020/
Despite near-surface enhancements in sulfate particles (Fig. 11) and SO2 mixing ratios observed by active DOAS (Fig. 5f), the MAX-DOAS and lidar AODs were very similar after 11:30–17:00 local time (LT) on 3 September (Fig. 5a)

Summary

Introduction

The Athabasca oil sands operations in Alberta contain significant sources of industrial atmospheric pollutants, such as sulfur dioxide (SO2) and nitrogen dioxide (NO2) (ECCC, 2018b, c). While the Athabasca oil sands region (AOSR) experiences moderate annual average concentrations of SO2 relative to all Canadian in situ stations, the short-term concentrations can be significantly higher than in most Canadian cities (Government of Canada, 2018). The AOSR contains some of the few monitoring sites in Canada that experience peak 1 h average concentrations of SO2 of greater than 70 ppb (Government of Canada, 2018), which is the new 2020 Canadian Ambient Air Quality Standard for SO2 (Canadian Council of Ministers of the Environment, 2014). Exposure to NO2 at high concentrations over the short term is associated with significant health impacts (WHO, 2006), and NOx (NO + NO2) is a precursor to tropospheric ozone (O3), acid rain, and fine particulate matter (Seinfeld and Pandis, 2006)

Objectives

Results

Conclusion