Enhancement of aerosol responses to changes in emissions over East Asia by gas‐oxidant‐aerosol coupling and detailed aerosol processes

Abstract

We quantify the responses of aerosols to changes in emissions (sulfur dioxide, black carbon (BC), primary organic aerosol, nitrogen oxides (NOx), and volatile organic compounds) over East Asia by using simulations including gas‐oxidant‐aerosol coupling, organic aerosol (OA) formation, and BC aging processes. The responses of aerosols to NOx emissions are complex and are dramatically changed by simulating gas‐phase chemistry and aerosol processes online. Reduction of NOx emissions by 50% causes a 30–40% reduction of oxidant (hydroxyl radical and ozone) concentrations and slows the formation of sulfate and OA by 20–30%. Because the response of OA to changes in NOx emissions is sensitive to the treatment of emission and oxidation of semivolatile and intermediate volatility organic compounds, reduction of the uncertainty in these processes is necessary to evaluate gas‐oxidant‐aerosol coupling accurately. Our simulations also show that the sensitivity of aerosols to changes in emissions is enhanced by 50–100% when OA formation and BC aging processes are resolved in the model. Sensitivity simulations show that the increase of NOx emissions from 1850 to 2000 explains 70% (40%) of the enhancement of aerosol mass concentrations (direct radiative effects) over East Asia during that period through enhancement of oxidant concentrations and that this estimation is sensitive to the representation of OA formation and BC aging processes. Our results demonstrate the importance of simultaneous simulation of gas‐oxidant‐aerosol coupling and detailed aerosol processes. The impact of NOx emissions on aerosol formation will be a key to formulating effective emission reduction strategies such as BC mitigation and aerosol reduction policies in East Asia.

Trends in Chemical Composition of Global and Regional Population-Weighted Fine Particulate Matter Estimated for 25 Years

“…Over 2006–2013, PWM PM 2.5 in East Asia insignificantly ( p > 0.1) decreases in Trend sat and Sim ds , despite significantly ( p < 0.05) increasing nitrate (0.28 μg m –3 yr –1 ). This recent reversal of PM 2.5 trends over China is consistent with other investigations , (SI Tables S1 and S2), and implies the role of nitrate in driving recent and future PM 2.5 trends over China − after recent reductions in SO 2 and sulfate . China has made progress in reducing NO x emissions after 2011 as observed by satellite observations, but reducing nitrate could also benefit from reductions in NH 3 emissions. ,,, …”

Observed and Modeled Mass Concentrations of Organic Aerosols and PM2.5 at Three Remote Sites around the East China Sea: Roles of Chemical Aging

“…) was assumed to be 2.5 times the original POA emission (Matsui and Koike, 2016 The domain setting for the model simulation was the same as for the East Asia case of Matsui et al (2014) (see their Fig. 2(b)), having a nested inner domain with a horizontal grid spacing of 60 km.…”

Simulated sensitivity of secondary organic aerosol in the South Coast Air Basin of California to nitrogen oxides and other chemical parameters

“…However, SOA yield decreases for NO x levels between 1 and 100 ppb. Three-dimensional modeling applications have considered the effect of NO x on SOA both globally and in specific regions (Tsigaridis and Kanakidou 2003;Megaritis et al 2013;Pye et al 2015;Zheng et al 2015;Matsui and Koike 2016;Zhao et al 2017) and from specific emission sources globally (Afshar-Mohajer and Henderson 2017).…”