Anthropogenic Effects on Biogenic Secondary Organic Aerosol Formation

Anthropogenic emissions alter biogenic secondary organic aerosol(SOA)formation from naturally emitted volatileorganic compounds(BVOCs).We review the major laboratory and field findings with regard to effects of anthropogenicpollutants(NO_(x),anthropogenic aerosols,SO_(2),NH_(3))on biogenic SOA formation.NO_(x) participate in BVOC oxidationthrough changing the radical chemistry and oxidation capacity,leading to a complex SOA composition and yield sensitivitytowards NO_(x) level for different or even specific hydrocarbon precursors.Anthropogenic aerosols act as an importantintermedium for gas-particle partitioning and particle-phase reactions,processes of which are influenced by the particlephase state,acidity,water content and thus associated with biogenic SOA mass accumulation.SO_(2)modifies biogenic SOAformation mainly through sulfuric acid formation and accompanies new particle formation and acid-catalyzedheterogeneous reactions.Some new SO_(2)-involved mechanisms for organosulfate formation have also been proposed.NH_(3)/amines,as the most prevalent base species in the atmosphere,influence biogenic SOA composition and modify theoptical properties of SOA.The response of SOA formation behavior to these anthropogenic pollutants varies amongdifferent BVOCs precursors.Investigations on anthropogenic-biogenic interactions in some areas of China that aresimultaneously influenced by anthropogenic and biogenic emissions are summarized.Based on this review,somerecommendations are made for a more accurate assessment of controllable biogenic SOA formation and its contribution tothe total SOA budget.This study also highlights the importance of controlling anthropogenic pollutant emissions witheffective pollutant mitigation policies to reduce regional and global biogenic SOA formation.

Water-soluble matter in PM_(2.5)in a coastal city over China:Chemical components,optical properties,and source analysis

Although marine and terrestrial emissions simultaneously affect the formation of atmospheric fine particles in coastal areas,knowledge on the optical properties and sources of water-soluble matter in these areas is still scarce.In this work,taking Qingdao,China as a typical coastal location,the chemical composition of PM_(2.5)duringwinter 2019was analyzed.Excitation-emission matrix fluorescence spectroscopy was combined with parallel factor analysis model to explain the components of water-soluble atmospheric chromophores of PM_(2.5).Our analysis indicated that NO_(3)^(-),NH_(4)^(+)and SO_(4)^(2-)ions accounted for 86.80%of the total ion mass,dominated by NO_(3)^(-).The ratio of[NO_(3)^(-)]/[SO_(4)^(2-)]was up to 2.42±0.84,suggesting thatmobile sources play an important role in local pollutants emission.The result of positive correlation between Abs_(365)with K^(+)suggests that biomass burning is an important source of water-soluble organic compounds(WSOC).Six types of fluorophores(C1-C6),all humic-like substances,were identified in WSOC.Humification index,biological index and fluorescence index in winter were 1.66±0.34,0.51±0.44 and 1.09±0.78,respectively,indicating that WSOC in Qingdao were mainly terrestrial organic matters.Overall,although the study area is close to the ocean,the contribution of terrestrial sources to PM_(2.5),especially vehicle exhaust and coal combustion,is still much higher than that of marine sources.Our study provides a more comprehensive understanding of chemical and optical properties of WSOC based on PM_(2.5)in coastal areas,and may provide ground for improving local air quality.

Effect of NOx and SO2 on the photooxidation of methylglyoxal:Implications in secondary aerosol formation

Methylglyoxal(CH3COCHO,MG),which is one of the most abundant α-dicarbonyl compounds in the atmosphere,has been reported as a major source of secondary organic aerosol(SOA).In this work,the reaction of MG with hydroxyl radicals was studied in a 500 L smog chamber at(293±3)K,atmospheric pressure,(18±2)%relative humidity,and under different NOx and SO2.Particle size distribution was measured by using a scanning mobility particle sizer(SMPS)and the results showed that the addition of SO2 can promote SOA formation,while different NOx concentrations have different influences on SOA production.High NOx suppressed the SOA formation,whereas the particle mass concentration,particle number concentration and particle geometric mean diameter increased with the increasing NOx concentration at low NOx concentration in the presence of SO2.In addition,the products of the OH-initiated oxidation of MG and the functional groups of the particle phase in the MG/OH/SO2 and MG/OH/NOx/SO2 reaction systems were detected by gas chromatography mass spectrometry(GC-MS)and attenuated total reflection fourier transformed infrared spectroscopy(ATR-FTIR)analysis.Two products,glyoxylic acid and oxalic acid,were detected by GC-MS.The mechanism of the reaction of MG and OH radicals that follows two main pathways,H atom abstraction and hydration,is proposed.Evidence is provided for the formation of organic nitrates and organic sulfate in particle phase from IR spectra.Incorporation of NOx and SO2 influence suggested that SOA formation from anthropogenic hydrocarbons may be more efficient in polluted environment.

Heterogeneous reaction of SO_(2) on CaCO_(3) particles:Different impacts of NO_(2) and acetic acid on the sulfite and sulfate formation

Despite the heterogeneous reaction of sulfur dioxide(SO_(2))on mineral dust particles significantly affects the atmospheric environment,the effect of acidic gases on the formation of sulfite and sulfate from this reaction is not particularly clear.In this work,using the in-situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)technique,we employed a mineral dust particle model(CaCO_(3))combined with NO_(2)and acetic acid to investigate their effects on the heterogeneous reaction of SO_(2)on CaCO_(3)particles.Itwas found that water vapor can promote the formation of sulfite and simulated radiation can facilitate the oxidation of sulfite to sulfate.The addition of NO_(2)or acetic acid to the reaction system altered the production of sulfate and sulfite accordingly.There was a synergistic effect between NO_(2)and SO_(2)that promoted the oxidation of sulfite to sulfate,and a competitive effect between acetic acid and SO_(2)that inhibited the formation of sulfite.Moreover,light and water vapor can also affect the heterogeneous reaction of SO_(2)with the coexistence ofmultiple gases.These findings improve our understanding of the effects of organic and inorganic gases and environmental factors on the formation of sulfite and sulfate in heterogeneous reactions.

Assessing the influence of environmental conditions on secondary organic aerosol formation from a typical biomass burning compound

The atmospheric chemistry in complex air pollution remains poorly understood.In order to probe how environmental conditions can impact the secondary organic aerosol(SOA)formation from biomass burning emissions,we investigated the photooxidation of 2,5-dimethylfuran(DMF)under different environmental conditions in a smog chamber.It was found that SO_(2)could promote the formation of SOA and increase the amounts of inorganic salts produced during the photooxidation.The formation rate of SOA and the corresponding SOA mass concentration increased gradually with the increasing DMF/OH ratio.The addition of(NH_(4))_(2)SO_(4)seed aerosol accelerated the SOA formation rate and significantly shortened the time for the reaction to reach equilibrium.Additionally,a relatively high illumination intensity promoted the formation of OH radicals and,correspondingly,enhanced the photooxidation of DMF.However,the enhancement of light intensity accelerated the aging of SOA,which led to a gradual decrease of the SOA mass concentration.This work shows that by having varying influence on atmospheric chemical reactions,the same environmental factor can affect SOA formation in different ways.The present study is helpful for us to better understand atmospheric complex pollution.

Role of water on the H-abstraction from methanol by ClO

The influence of a single water molecule on the reaction mechanism and kinetics of hydrogen abstraction from methanol （CH3OH） by the CIO radical has been investigated using ab initio calculations. The reaction proceeds through two channels： abstraction of the hydroxyl H-atom and methyl H-atom of CH30H by CIO, leading to the formation of CH30 ＋ HOC1 （＋H20） and CH20H ＋ HOC1 （＋ H20）, respectively. In both cases, pre- and post-reactive complexes were located at the entrance and exit channel on the potential energy surfaces. Results indicate that the formation of CH2OH ＋ HOC1 （＋H20） is predominant over the formation of CH30 ＋ HOC1 （＋H20）, with ambient rate constants of 3.07 x 10^-19 and 3.01 x 10^-23 cm^3/（molecule.sec）, respectively, for the reaction without water. Over the temperature range 216.7-298.2 K, the presence of water is seen to effectively lower the rate constants for the most favorable pathways by 4-6 orders of magnitude in both cases. It is therefore concluded that water plays an inhibitive role on the CH30H ＋ ClO reaction under tropospheric conditions.