Insights into seasonal variation of wet deposition over southeast Asia via precipitation adjustment from the findings of MICS-Asia III

Abstract

Abstract. Asia has attracted research attention because it has the highest anthropogenic emissions in the world, and the Model Inter-Comparison Study for Asia (MICS-Asia) phase III was carried out to foster our understanding of the status of air quality over Asia. This study analyzed wet deposition in southeast Asian countries (Myanmar, Thailand, Lao People's Democratic Republic (PDR), Cambodia, Vietnam, the Philippines, Malaysia, and Indonesia) with the aim of providing insights into the seasonal variation of wet deposition. Southeast Asia was not fully considered in MICS-Asia phase II due to a lack of observational data; however, the analysis period of MICS-Asia III, namely the year 2010, is covered by ground observations of the Acid Deposition Monitoring Network in East Asia (EANET), and the coordinated simulation domain was extended to cover these observation sites. The analyzed species are wet depositions of S (sulfate aerosol, sulfur dioxide (SO2), and sulfuric acid (H2SO4)), N (nitrate aerosol, nitrogen monoxide (NO), nitrogen dioxide (NO2), and nitric acid (HNO3)), and A (ammonium aerosol and ammonia (NH3)). The wet deposition simulated with seven models driven by a unified meteorological model in MICS-Asia III was used with the ensemble approach, which effectively modulates the differences in performance among models. By comparison with EANET observations, although the seven models generally captured the wet depositions of S, N, and A, there were difficulties capturing these in some cases. Considering the model performance for ambient aerosol concentrations over southeast Asia, this failure of models is considered to be related to the difficulty in capturing the precipitation in southeast Asia, especially during the dry and wet seasons. Generally, meteorological fields overestimate the precipitation during the dry season, which leads to the overestimation of wet deposition during this season. To overcome this, a precipitation-adjusted approach that scaled the modeled precipitation to the observed value was applied, and it was demonstrated that the model performance was improved. Satellite measurements were also used to adjust for precipitation data, which adequately accounted for the spatiotemporal precipitation patterns, especially in the dry season. As the statistical scores were mostly improved by this adjustment, the estimation of wet deposition with precipitation adjustment was considered to be superior. To utilize satellite measurements, the spatial distribution of wet deposition was revised. Based on this revision, it was found that Vietnam, Malaysia, and Indonesia were upward corrected, and Myanmar, Thailand, Lao PDR, Cambodia, and the Philippines were downward-corrected; these corrections were up to ±40 %. The improved accuracy of precipitation amount was key to estimating wet deposition in this study. These results suggest that the precipitation-adjusted approach has the potential to obtain accurate estimates of wet deposition through the fusion of models and observations.

The impact of biomass burning emissions on aerosol concentrations and depositions in the northern South China Sea region

“…This is consistent with previous studies. For example, Itahashi et al (2021) have investigated the seasonal variation of wet deposition over Southeast Asia based on observations and model simulations. They showed that wet depositions of aerosol components were much smaller in winter and spring than those in summer and autumn in MSEA areas such as Thailand, Vietnam, and Cambodia.…”

Improving Below‐Cloud Scavenging Coefficients of Sulfate, Nitrate, and Ammonium in PM2.5 and Implications for Numerical Simulation and Air Pollution Control

“…BS coefficient for aerosol (specially referred to as Λ hereafter), the key in characterizing aerosol BS process, is parametrized diversely in CTMs, reflecting variations in the limited observations (Chin et al., 2000; Lu & Fung, 2018). This inevitably causes differences in simulated aerosol burden (Croft et al., 2009, 2010; Lu & Fung, 2018; Textor et al., 2006) and wet deposition (Ge et al., 2020; Itahashi et al., 2020, 2021; Z. Wang et al., 2008), and then limits the accurate assessments of their climate (Choi et al., 2020; J. Xu et al., 2019) and ecological effects (Vivanco et al., 2018). Specifically, the Λ for fine particle (PM 2.5 ) in CTMs (10 −6 –10 −5 s −1 ) is mostly 1–2 orders of magnitudes lower than measurements (10 −5 –10 −4 s −1 ) (Ge et al., 2021; D. Xu et al., 2019), which probably leads to an underestimation of BS.…”

“…Specifically, the Λ for fine particle (PM 2.5 ) in CTMs (10 −6 –10 −5 s −1 ) is mostly 1–2 orders of magnitudes lower than measurements (10 −5 –10 −4 s −1 ) (Ge et al., 2021; D. Xu et al., 2019), which probably leads to an underestimation of BS. This underestimation is responsible for underpredicting wet deposition for $${\text{SO}}_{4}^{2\mbox{--}}$$, $${\text{NO}}_{3}^{\mbox{--}}$$, and $${\text{NH}}_{4}^{+}$$ (SNA) in East Asia (medians for corresponding species: 32%–64%, 9%–55%, and 10%–16%) (Ge et al., 2020; Itahashi et al., 2020, 2021; Luo et al., 2020), Europe (12%–58%, 20%–31%, and 19%–33%) (Dentener et al., 2006; Luo et al., 2020; Simpson et al., 2006; Theobald et al., 2019; Vet et al., 2014; Vivanco et al., 2018) and the USA (21%–35%, 53%–68%, and 10%–48%) (Luo et al., 2020; Nopmongcol et al., 2019; Vet et al., 2014; Y. Zhang et al., 2018).…”

“…Xu et al, 2019), which probably leads to an underestimation of BS. This underestimation is responsible for underpredicting wet deposition for 𝐴𝐴 SO 2-4 , 𝐴𝐴 NO -3 , and 𝐴𝐴 NH + 4 (SNA) in East Asia (medians for corresponding species: 32%-64%, 9%-55%, and 10%-16%) (Ge et al, 2020;Itahashi et al, 2020Itahashi et al, , 2021Luo et al, 2020), Europe (12%-58%, 20%-31%, and 19%-33%) (Dentener et al, 2006;Luo et al, 2020;Simpson et al, 2006;Theobald et al, 2019;Vet et al, 2014;Vivanco et al, 2018) and the USA (21%-35%, 53%-68%, and 10%-48%) (Luo et al, 2020;Nopmongcol et al, 2019;Vet et al, 2014;.…”

“…BS coefficient for aerosol (specially referred to as Λ hereafter), the key in characterizing aerosol BS process, is parametrized diversely in CTMs, reflecting variations in the limited observations (Chin et al, 2000;Lu & Fung, 2018). This inevitably causes differences in simulated aerosol burden (Croft et al, 2009(Croft et al, , 2010Lu & Fung, 2018;Textor et al, 2006) and wet deposition (Ge et al, 2020;Itahashi et al, 2020Itahashi et al, , 2021Z. Wang et al, 2008), and then limits the accurate assessments of their climate (Choi et al, 2020;J.…”