Jianwei Gu

Formation and evolution mechanism of regional haze: a case study in the megacity Beijing, China

The main objective of this study is to investigate the formation and evolution mechanism of the regional haze in megacity Beijing by analyzing the process of a severe haze that occurred 20–27 September 2011. Mass concentration and size distribution of aerosol particles as well as aerosol optical properties were concurrently measured at the Beijing urban atmospheric environment monitoring station. Gaseous pollutants (SO 2, NO-NO2-NOx, O3, CO) and meteorological parameters (wind speed, wind direction, and relative humidity) were simultaneously monitored. Meanwhile, aerosol spatial distribution and the height of planetary boundary layer (PBL) were retrieved from the signal of satellite and LIDAR (light detection and ranging). Concentrations of NO, NO2, SO2, O3, and CO observed during 23–27 September had exceeded the national ambient air quality standards for residents. The mass concentration of PM 2.5 gradually accumulated during the measurement and reached at 220 μg m −3 on 26 September, and the corresponding atmospheric visibility was only 1.1 km. The daily averaged AOD in Beijing increased from∼ 0.16 atλ = 500 nm on 22 September and reached∼ 3.5 on 26 September. The key factors that affected the formation and evolution of this haze episode were stable anti-cyclone synoptic conditions at the surface, decreasing of the height of PBL, heavy pollution emissions from urban area, number and size evolution of aerosols, and hygroscopic growth for aerosol scattering. This c se study may provide valuable information for the public to recognize the formation mechanism of the regional haze event over the megacity, which is also useful for the government to adopt scientific approach to forecast and eliminate the occurrence of regional haze in China.

Aerosol chemistry and the effect of aerosol water content on visibility impairment and radiative forcing in Guangzhou during the 2006 Pearl River Delta campaign

Optical and chemical aerosol measurements were obtained from 2 to 31 July 2006 at an urban site in the metropolitan area of Guangzhou (China) as part of the Program of Regional Integrated Experiment of Air Quality over Pearl River Delta (PRIDE-PRD2006) to investigate aerosol chemistry and the effect of aerosol water content on visibility impairment and radiative forcing. During the PRIDE-PRD2006 campaign, the average contributions of ammonium sulfate, organic mass by carbon (OMC), elemental carbon (EC), and sea salt (SS) to total PM(2.5) mass were measured to be 36.5%, 5.7%, 27.1%, 7.8%, and 3.7%, respectively. Compared with the clean marine period, (NH(4))(2)SO(4), NH(4)NO(3), and OMC were all greatly enhanced (by up to 430%) during local haze periods via the accumulation of a secondary aerosol component. The OMC dominance increased when high levels of biomass burning influenced the measurement site while (NH(4))(2)SO(4) and OMC did when both biomass burning and industrial emissions influenced it. The effect of aerosol water content on the total light-extinction coefficient was estimated to be 34.2%, of which 25.8% was due to aerosol water in (NH(4))(2)SO(4), 5.1% that in NH(4)NO(3), and 3.3% that in SS. The average mass-scattering efficiency (MSE) of PM(10) particles was determined to be 2.2+/-0.6 and 4.6+/-1.7m(2)g(-1) under dry (RH<40%) and ambient conditions, respectively. The average single-scattering albedo (SSA) was 0.80+/-0.08 and 0.90+/-0.04 under dry and ambient conditions, respectively. Not only are the extinction and scattering coefficients greatly enhanced by aerosol water content, but MSE and SSA are also highly sensitive. It can be concluded that sulfate and carbonaceous aerosol, as well as aerosol water content, play important roles in the processes that determine visibility impairment and radiative forcing in the ambient atmosphere of the Guangzhou urban area.

Particle-associated organic compounds and symptoms in myocardial infarction survivors

Context: The aerosol components responsible for the adverse health effects of the exposure to particulate matter (PM) have not been conclusively identified, and there is especially little information on the role of particulate organic compounds (POC). Objective: This study evaluated the role of PM and POC with regard to daily symptoms. Methods: One hundred and fifty-three myocardial infarction survivors from Augsburg, Germany, recorded daily occurrence of different symptoms in winter 2003/2004. Ambient concentrations of PM with a diameter <2.5 μm (PM2.5), particle number concentration (PNC), PM2.5-bound hopanes, and polycyclic aromatic hydrocarbons (PAH) were quantified. Data were analyzed using generalized estimating equations adjusting for meteorological and other time-variant confounders. Results: The odds for avoidance of physically demanding activities due to heart problems increased immediately associated with most POC measures (e.g. 5% per 1.08 ng/m3 increase in benzo[a]pyrene, 95%-confidence interval (CI):1–9%) and tended to a delayed decrease. After a 2-day delayed decrease associated with hopanes, the odds for shortness of breath increased consistently after 3 days with almost all POC measures (e.g. 4% per 0.21 ng/m3 increase in 17α(H), 21β(H)-hopane, CI: 1–8%). The odds for heart palpitations marginally increased immediately in association with PNC (8% per 8146 cm−3 increase in PNC, CI: 0–16%). Conclusions: The study showed an association between PM, particle-bound POC, and daily symptoms. The organic compounds may be causally related with cardiovascular health or act rather as indicators for traffic- and combustion-related particles.

Chemical characterization of size-resolved aerosols in four seasons and hazy days in the megacity Beijing of China

Size-resolved aerosol samples were collected by MOUDI in four seasons in 2007 in Beijing. The PM10 and PM1.8 mass concentrations were 166.0±120.5 and 91.6±69.7 μg/m3, respectively, throughout the measurement, with seasonal variation: nearly two times higher in autumn than in summer and spring. Serious fine particle pollution occurred in winter with the PM1.8/PM10 ratio of 0.63, which was higher than other seasons. The size distribution of PM showed obvious seasonal and diurnal variation, with a smaller fine mode peak in spring and in the daytime. OM (organic matter=1.6×OC (organic carbon)) and SIA (secondary inorganic aerosol) were major components of fine particles, while OM, SIA and Ca2+ were major components in coarse particles. Moreover, secondary components, mainly SOA (secondary organic aerosol) and SIA, accounted for 46%-96% of each size bin in fine particles, which meant that secondary pollution existed all year. Sulfates and nitrates, primarily in the form of (NH4)2SO4, NH4NO3, CaSO4, Na2SO4 and K2SO4, calculated by the model ISORROPIA II, were major components of the solid phase in fine particles. The PM concentration and size distribution were similar in the four seasons on non-haze days, while large differences occurred on haze days, which indicated seasonal variation of PM concentration and size distribution were dominated by haze days. The SIA concentrations and fractions of nearly all size bins were higher on haze days than on non-haze days, which was attributed to heterogeneous aqueous reactions on haze days in the four seasons.

Chemical characteristics of size-resolved aerosols in winter in Beijing

Size-resolved aerosols were continuously collected by a Nano Sampler for 13 days at an urban site in Beijing during winter 2012 to measure the chemical composition of ambient aerosol particles. Data collected by the Nano Sampler and an ACSM (Aerodyne Aerosol Chemical Speciation Monitor) were compared. Between the data sets, similar trends and strong correlations were observed, demonstrating the validity of the Nano Sampler. PM₁₀ and PM₂.₅ concentrations during the measurement were 150.5 ± 96.0 μg/m³ (mean ± standard variation) and 106.9 ± 71.6 μg/m³, respectively. The PM₂.₅/PM₁₀ ratio was 0.70 ± 0.10, indicating that PM₂.₅ dominated PM₁₀. The aerosol size distributions showed that three size bins of 0.5-1, 1-2.5 and 2.5-10 μm contributed 21.8%, 23.3% and 26.0% to the total mass concentration (TMC), respectively. OM (organic matter) and SIA (secondary ionic aerosol, mainly SO₄(2-), NO₃(-) and NH₄(+)) were major components of PM₂.₅. Secondary compounds (SIA and secondary organic carbon) accounted for half of TMC (about 49.8%) in PM₂.₅, and suggested that secondary aerosols significantly contributed to the serious particulate matter pollution observed in winter. Coal burning, biomass combustion, vehicle emissions and SIA were found to be the main sources of PM₂.₅. Mass concentrations of water-soluble ions and undetected materials, as well as their fractions in TMC, strikingly increased with deteriorating particle pollution conditions, while OM and EC (elemental carbon) exhibited different variations, with mass concentrations slightly increasing but fractions in TMC decreasing.

Daytime HONO formation in the suburban area of the megacity Beijing, China

Nitrous acid (HONO), as a primary precursor of OH radicals, has been considered one of the most important nitrogen-containing species in the atmosphere. Up to 30% of primary OH radical production is attributed to the photolysis of HONO. However, the major HONO formation mechanisms are still under discussion. During the Campaigns of Air Quality Research in Beijing and Surrounding Region (CAREBeijing2006) campaign, comprehensive measurements were carried out in the megacity Beijing, where the chemical budget of HONO was fully constrained. The average diurnal HONO concentration varied from 0.33 to 1.2 ppbv. The net OH production rate from HONO, POH(HONO)net, was on average (from 05:00 to 19:00 h) 7.1 × 106 molecule/(cm3 s), 2.7 times higher than from O3 photolysis. This production rate demonstrates the important role of HONO in the atmospheric chemistry of megacity Beijing. An unknown HONO source (Punknown) with an average of 7.3 × 106 molecule/(cm3 s) was derived from the budget analysis during daytime. Punknown provided four times more HONO than the reaction of NO with OH did. The diurnal variation of Punknown showed an apparent photo-enhanced feature with a maximum around 12:00 h, which was consistent with previous studies at forest and rural sites. Laboratory studies proposed new mechanisms to recruit NO2 and J(NO2) in order to explain a photo-enhancement of of Punknown. In this study, these mechanisms were validated against the observation-constraint Punknown. The reaction of exited NO2 accounted for only 6% of Punknown, and Punknown poorly correlated with [NO2] (R = 0.26) and J(NO2)[NO2] (R = 0.35). These results challenged the role of NO2 as a major precursor of the missing HONO source.