Simultaneous observations by sky radiometer and MAX-DOAS for characterization of biomass burning plumes in central Thailand in January–April 2016

Hitoshi Irie,Alessandro Damiani,Pradeep Khatri,Al Mashroor Fatmi,Thanawat Jarupongsakul,Tamio Takamura,Hiroshi Okamoto,Hossain Mohammed Syedul Hoque

doi:10.5194/amt-12-599-2019

Abstract

Abstract. The first intensive multicomponent ground-based remote-sensing observations by sky radiometer and multi-axis differential optical absorption spectroscopy (MAX-DOAS) were performed simultaneously at the SKYNET Phimai site located in central Thailand (15.18∘ N, 102.56∘ E) from January to April 2016. The period corresponds to the dry season associated with intense biomass burning (BB) activity around the site. The near-surface concentration of formaldehyde (HCHO) retrieved from MAX-DOAS was found to be a useful tracer for absorption aerosols from BB plumes, when BB was the dominant source of HCHO and absorption aerosols over other sources. As the HCHO concentration tripled from 3 to 9 ppbv, the ratio of gaseous glyoxal to HCHO concentrations in daytime decreased from ∼0.04 to ∼0.03, responding presumably to the increased contribution of volatile organic compound emissions from BB. In addition, clear increases in aerosol absorption optical depths (AAODs) retrieved from sky radiometer observations were seen with the HCHO enhancement. At a HCHO of 9 ppbv, AAOD at a wavelength of 340 nm reached as high as ∼0.15±0.03. The wavelength dependence of AAODs at 340–870 nm was quantified by the absorption Ångström exponent (AAE), providing evidence for the presence of brown carbon aerosols at an AAE of 1.5±0.2. Thus, our multicomponent observations around central Thailand are expected to provide unique constraints for understanding physical–chemical–optical properties of BB plumes.

Highlights

It is well recognized that aerosols contribute the largest uncertainty to the estimate of radiative forcing (e.g., IPCC, 2013)
The RGF is important for atmospheric chemistry as it would vary responding to different volatile organic compounds (VOCs) emissions such as Biomass burning (BB) and biogenic activities (e.g., Hoque et al, 2018a, b)
As the HCHO concentration tripled from 3 to 9 ppbv, the RGF decreased from ∼ 0.04 to ∼ 0.03 and the NO2 concentration doubled from ∼ 0.6 to ∼ 1.2 ppbv, responding presumably to the increased contribution of VOC emissions from BB

Summary

Introduction

It is well recognized that aerosols contribute the largest uncertainty to the estimate of radiative forcing (e.g., IPCC, 2013). About two-thirds of the global primary organic aerosol (OA) that should comprise a large amount of ultraviolet (UV)-light-absorbing OA, known as brown carbon (BrC), originates from BB plumes (Bond et al, 2013). Underestimation in aerosol absorption over most BB regions was reported by Hammer et al (2016), who used a global 3-D chemistry transport model (GEOS-Chem), in which OA is regarded as purely scattering. Characterization for the BB plumes is attempted using our unique remote-sensing observations by the sky radiometer (e.g., Nakajima et al, 1996) and the multi-axis differential optical absorption spectroscopy (MAX-DOAS) (e.g., Irie et al, 2011) for both viewpoints of the optical properties of aerosols (aerosol absorption optical depth, AAOD, and absorption Ångström exponent, AAE) and the organic gas concentrations (formaldehyde, HCHO, and glyoxal, CHOCHO) in BB plumes

Observation

Sky radiometer observation of aerosol optical properties

MAX-DOAS observation of trace gases

Results and discussion

Conclusions