The photolysis of nitrous acid (HONO) in the early morning hours is an important source of OH radicals, the most important daytime oxidizing species. Although the importance of this mechanism has been recognized for many years, no accurate quantification of this OH source is available, and the role of HONO photolysis is often underestimated. We present measurements of HONO and its precursor NO 2 by Differential Optical Absorption Spectroscopy (DOAS) during the Berliner Ozonexperiment (BERLIOZ) field campaign in July/August 1998 at Pabstthum near Berlin, Germany. HONO concentrations, formation rates, and simultaneously measured HONO photolysis frequencies are used to calculate the total amount of OH formed by HONO photolysis during a full diurnal cycle. A comparison with the OH formation by photolysis of O 3 and HCHO and by the reaction of alkenes with ozone shows that HONO photolysis contributed up to 20% of the total OH formed in a 24 hour period during this campaign. In the morning hours, HONO photolysis was by far the most important OH source during BERLIOZ.

OH formation by HONO photolysis during the BERLIOZ experiment : Photochemistry experiment in BERLIOZ (PHOEBE)

Ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements of nitrous acid (HONO) and its precursor NO2 (nitrogen dioxide) as well as aerosols have been performed daily in Beijing city centre (39.98° N, 116.38° E) from July 2008 to April 2009 and at the suburban site of Xianghe (39.75° N, 116.96° E) located ~60 km east of Beijing from March 2010 to December 2012. This extensive dataset allowed for the first time the investigation of the seasonal cycle of HONO as well as its diurnal variation in and in the vicinity of a megacity. Our study was focused on the HONO and NO2 near-surface concentrations (0–200 m layer) and total vertical column densities (VCDs) and also aerosol optical depths (AODs) and extinction coefficients retrieved by applying the Optimal Estimation Method to the MAX-DOAS observations. Monthly averaged HONO near-surface concentrations at local noon display a strong seasonal cycle with a maximum in late fall/winter (~0.8 and 0.7 ppb at Beijing and Xianghe, respectively) and a minimum in summer (~0.1 ppb at Beijing and 0.03 ppb at Xianghe). The seasonal cycles of HONO and NO2 appear to be highly correlated, with correlation coefficients in the 0.7–0.9 and 0.5–0.8 ranges at Beijing and Xianghe, respectively. The stronger correlation of HONO with NO2 and also with aerosols observed in Beijing suggests possibly larger role of NO2 conversion into HONO in the Beijing city center than at Xianghe. The observed diurnal cycle of HONO near-surface concentration shows a maximum in the early morning (about 1 ppb at both sites) likely resulting from night-time accumulation, followed by a decrease to values of about 0.1–0.4 ppb around local noon. The HONO / NO2 ratio shows a similar pattern with a maximum in the early morning (values up to 0.08) and a decrease to ~0.01–0.02 around local noon. The seasonal and diurnal cycles of the HONO near-surface concentration are found to be similar in shape and in relative amplitude to the corresponding cycles of the HONO total VCD and are therefore likely driven mainly by the balance between HONO sources and the photolytic sink, whereas dilution effects appear to play only a minor role. The estimation of OH radical production from HONO and O3 photolysis based on retrieved HONO near-surface concentrations and calculated photolysis rates indicate that in the 0–200 m altitude range, HONO is by far the largest source of OH radicals in winter as well as in the early morning at all seasons, while the contribution of O3 dominates in summer from mid-morning until mid-afternoon.

Four Years of Ground-based MAX-DOAS Observations of HONO and NO2 in the Beijing Area

Characteristics and sources of volatile organic compounds (VOCs) in Shanghai during summer: Implications of regional transport

 The predominating role of aerosol Fuchs surface area, AFuchs, in determining the occurrence of new particle formation (NPF) events in Beijing was elucidated in this study The analysis was based on a field campaign from 12 March to 6 April 2016 in Beijing, during which aerosol size distributions down to  ∼  1 nm and sulfuric acid concentrations were simultaneously monitored The 26 days were classified into 11 typical NPF days, 2 undefined days, and 13 non-event days A dimensionless factor, LΓ, characterized by the relative ratio of the coagulation scavenging rate over the condensational growth rate (Kuang et al, 2010), was applied in this work to reveal the governing factors for NPF events in Beijing The three parameters determining LΓ are sulfuric acid concentration, the growth enhancement factor characterized by contribution of other gaseous precursors to particle growth, Γ, and AFuchs Different from other atmospheric environments, such as in Boulder and Hyytiala, the daily-maximum sulfuric acid concentration and Γ in Beijing varied in a narrow range with geometric standard deviations of 140 and 131, respectively A positive correlation between the estimated new particle formation rate, J15, and sulfuric acid concentration was found with a mean fitted exponent of 24 However, the maximum sulfuric acid concentrations on NPF days were not significantly higher (even lower, sometimes) than those on non-event days, indicating that the abundance of sulfuric acid in Beijing was high enough to initiate nucleation, but may not necessarily lead to NPF events Instead, AFuchs in Beijing varied greatly among days with a geometric standard deviation of 256, whereas the variabilities of AFuchs in Tecamac, Atlanta, and Boulder were reported to be much smaller In addition, there was a good correlation between AFuchs and LΓ in Beijing (R2 = 088) Therefore, it was AFuchs that fundamentally determined the occurrence of NPF events Among 11 observed NPF events, 10 events occurred when AFuchs was smaller than 200 µm2 cm−3 NPF events were suppressed due to the coagulation scavenging when AFuchs was greater than 200 µm2 cm−3 Measured AFuchs in Beijing had a good correlation with its PM25 mass concentration (R2 = 085) since AFuchs in Beijing was mainly determined by particles in the size range of 50–500 nm that also contribute to the PM25 mass concentration

/pdf/aerosol-surface-area-concentration-a-governing-factor-in-new-55r8w6vb4t.pdf

Aerosol surface area concentration: a governing factor in new particle formation in Beijing

https://link.springer.com/content/pdf/10.1007/s13361-019-02209-3.pdf

A Library of Proton-Transfer Reactions of H3O+ Ions Used for Trace Gas Detection

. A proton transfer reaction ion-drift chemical ionization mass spectrometer (PTR-ID-CIMS) equipped with a hydronium (H3+O) ion source was developed and deployed near an industrial zone in the Yangtze River Delta (YRD) region of China in spring 2015 to investigate industry-related emissions of volatile organic compounds (VOCs). Air pollutants including formaldehyde (HCHO), aromatics, and other trace gases (O3 and CO) were simultaneously measured. Humidity effects on the sensitivity of the PTR-ID-CIMS for HCHO detection were investigated and quantified. The performances of the PTR-ID-CIMS were also validated by intercomparing with offline HCHO measurement technique using 2,4-dinitrophenylhydrazone (DNPH) cartridges and the results showed fairly good agreement (slope  =  0.81, R2  =  0.80). The PTR-ID-CIMS detection limit of HCHO (10 s, three-duty-cycle averages) was determined to be 0.9–2.4 (RH  =  1–81.5 %) parts per billion by volume (ppbv) based on 3 times the standard deviations of the background signals. During the field study, observed HCHO concentrations ranged between 1.8 and 12.8 ppbv with a campaign average of 4.1 ± 1.6 ppbv, which was comparable with previous HCHO observations in other similar locations of China. However, HCHO diurnal profiles showed few features of secondary formation. In addition, time series of both HCHO and aromatic VOCs indicated strong influence from local emissions. Using a multiple linear regression fit model, on average the observed HCHO can be attributed to secondary formation (13.8 %), background level (27.0 %), and industry-related emissions, i.e., combustion sources (43.2 %) and chemical productions (16.0 %). Moreover, within the plumes the industry-related emissions can account for up to 69.2 % of the observed HCHO. This work has provided direct evidence of strong primary emissions of HCHO from industry-related activities. These primary HCHO sources can potentially have a strong impact on local and regional air pollution formation in this area of China. Given the fact that the YRD is the largest economic zone in China and is dense with petrochemical industries, primary industrial HCHO emissions should be strictly monitored and regulated.

/pdf/detection-of-formaldehyde-emissions-from-an-industrial-zone-58fuyrhda1.pdf

Detection of formaldehyde emissions from an industrial zone in the Yangtze River Delta region of China using a proton transfer reaction ion-drift chemical ionization mass spectrometer

Detection of formaldehyde emissions from an industrial zone in the

. A suite of instruments was deployed to simultaneously measure nitrous acid
(HONO), nitrogen oxides ( NOx = NO + NO2 ), carbon monoxide
(CO), ozone ( O3 ), volatile organic compounds (VOCs – including
formaldehyde, HCHO) and meteorological parameters near a typical industrial
zone in Nanjing in the Yangtze River Delta (YRD) region of China from 1 to 31 December 2015. High levels of HONO were detected using a wet-chemistry-based
method. HONO ranged from 0.03 to 7.04 ppbv with an average of 1.32±0.92  ppbv. Elevated daytime HONO was frequently observed with a minimum of
several hundred parts per trillion by volume (pptv) on average, which cannot be explained by the
homogeneous OH + NO reaction ( POH+NO ) and primary emissions
( Pemission ), especially during periods with high particulate matter (PM 2.5 ) loadings. HONO chemistry and its impact on the
atmospheric oxidation capacity in the study area were further investigated
using a Master Chemical Mechanism (MCM) box model. The results show that the
average hydroxyl radical (OH) production rate was dominated by the
photolysis of HONO ( 7.13×106  molec. cm −3  s −1 ),
followed by the ozonolysis of alkenes ( 3.94×106  molec. cm −3  s −1 ), the photolysis of O3 ( 2.46×106  molec. cm −3  s −1 ) and the photolysis of HCHO ( 1.60×106  molec. cm −3  s −1 ) during the campaign period, especially within plumes that
originated from the industrial zone. Model simulations indicated that
heterogeneous chemistry played an important role in HONO formation. The
average nighttime NO2 to HONO conversion rate was determined to
be ∼0.8  % h −1 . A good correlation between nocturnal
 HONO∕NO2 and the product of particle surface area density ( S∕V ) and
relative humidity (RH), S / V ⋅ RH , supports the heterogeneous
 NO2∕H2O reaction mechanism. The other HONO source, designated as
 Punknonwn , was about twice as high as POH+NO on average and
displayed a diurnal profile with an evidently photo-enhanced feature, i.e.,
photosensitized reactions of NO2 may be an important daytime HONO
source. Nevertheless, our results suggest that daytime HONO formation was
mostly due to the light-induced conversion of NO2 on aerosol surfaces,
whereas heterogeneous NO2 reactions on the ground surface dominated nocturnal
HONO production. Our study indicated that an elevated PM 2.5 level during haze events can promote the conversion of NO2 to HONO by providing more
heterogeneous reaction sites, thereby increasing the atmospheric oxidation
capacity, which may further promote the formation of secondary air
pollutants. Highlights: High levels of HONO, with an average of 1.32±0.92  ppbv, were
observed near one of the largest industrial zones in the YRD region of
China. HONO photolysis and alkene ozonolyses contributed the most to OH production
and, hence, the atmospheric oxidation capacity. High loading of PM 2.5 provided additional reaction surfaces for HONO
formation. Heterogeneous formation mechanisms were the most important daytime HONO
sources and were further enhanced by sunlight.

/pdf/contribution-of-nitrous-acid-to-the-atmospheric-oxidation-1m6ljan3ud.pdf

Contribution of nitrous acid to the atmospheric oxidation capacity in an industrial zone in the Yangtze River Delta region of China

On-line measurement of fluorescent aerosols near an industrial zone in the Yangtze River Delta region using a wideband integrated bioaerosol spectrometer

Weiwei Wang

Papers

Detection of formaldehyde emissions from an industrial zone in the Yangtze River Delta region of China using a proton transfer reaction ion-drift chemical ionization mass spectrometer

Detection of formaldehyde emissions from an industrial zone in the

Contribution of nitrous acid to the atmospheric oxidation capacity in an industrial zone in the Yangtze River Delta region of China

On-line measurement of fluorescent aerosols near an industrial zone in the Yangtze River Delta region using a wideband integrated bioaerosol spectrometer